Update name of main branch in CI and docs (#161)

The name of the main branch is now "main".
Documentation and CI scripts are updated accordingly.

Co-authored-by: Ryan Burns <rtburns-jpl@users.noreply.github.com>

.circleci/config.yml

@@ -247,13 +247,13 @@ workflows:
       - build:
           filters:
             branches:
-              only: master
+              only: main
       - deploy:
           requires:
             - build
           filters:
             branches:
-              only: master
+              only: main
   build-deploy-release:
     jobs:
       - build-release:
@@ -277,15 +277,15 @@ workflows:
           filters:
             branches:
               only:
-                - master
+                - main
     jobs:
       - build-periodically:
           filters:
             branches:
-              only: master
+              only: main
       - deploy:
           requires:
             - build-periodically
           filters:
             branches:
-              only: master
+              only: main

CONTRIBUTING.md

@@ -45,19 +45,19 @@ cd isce2
 git remote add my_user_name https://github.com/my_user_name/isce2.git
 ```
 
-### Updating your local master against upstream master
+### Updating your local main branch against upstream
 
 ```
-git checkout master
+git checkout main
 git fetch origin
-# Be careful: this will loose all local changes you might have done now
-git reset --hard origin/master
+# Be careful: this will lose all local changes you might have done now
+git reset --hard origin/main
 ```
 
 ### Working with a feature branch
 
 ```
-git checkout master
+git checkout main
 (potentially update your local reference against upstream, as described above)
 git checkout -b my_new_feature_branch
 
@@ -67,22 +67,22 @@ git add my_modifid_message
 git rm old_file
 git commit -a 
 
-# you may need to resynchronize against master if you need some bugfix
-# or new capability that has been added to master since you created your
+# you may need to resynchronize against main if you need some bugfix
+# or new capability that has been added to main since you created your
 # branch
 git fetch origin
-git rebase origin/master
+git rebase origin/main
 
 # At end of your work, make sure history is reasonable by folding non
 # significant commits into a consistent set
-git rebase -i master (use 'fixup' for example to merge several commits together,
+git rebase -i main (use 'fixup' for example to merge several commits together,
 and 'reword' to modify commit messages)
 
 # or alternatively, in case there is a big number of commits and marking
 # all them as 'fixup' is tedious
 git fetch origin
-git rebase origin/master
-git reset --soft origin/master
+git rebase origin/main
+git reset --soft origin/main
 git commit -a -m "Put here the synthetic commit message"
 
 # push your branch
@@ -93,7 +93,7 @@ From GitHub UI, issue a pull request
 If the pull request discussion results in changes,
 commit locally and push. To get a reasonable history, you may need to
 ```
-git rebase -i master
+git rebase -i main
 ```
 , in which case you will have to force-push your branch with 
 ```

docker/Dockerfile

@@ -71,7 +71,7 @@ RUN set -ex \
  && cd /tmp \
  && mkdir -p /tmp/rpm-build/opt \
  && mv $ISCE_INSTALL_ROOT /tmp/rpm-build/opt \
- && curl -s https://api.github.com/repos/$ISCE_ORG/isce2/git/refs/heads/master \
+ && curl -s https://api.github.com/repos/$ISCE_ORG/isce2/git/refs/heads/main \
     > /tmp/rpm-build/opt/isce2/version.json \
  && hash=$(cat /tmp/rpm-build/opt/isce2/version.json | jq -r .object.sha) \
  && short_hash=$(echo $hash | cut -c1-5) \

docker/Dockerfile.cuda

@@ -72,7 +72,7 @@ RUN set -ex \
  && rm -rf /opt/isce2/src \
  && mkdir -p /tmp/rpm-build/opt \
  && mv $ISCE_INSTALL_ROOT /tmp/rpm-build/opt \
- && curl -s https://api.github.com/repos/$ISCE_ORG/isce2/git/refs/heads/master \
+ && curl -s https://api.github.com/repos/$ISCE_ORG/isce2/git/refs/heads/main \
     > /tmp/rpm-build/opt/isce2/version.json \
  && hash=$(cat /tmp/rpm-build/opt/isce2/version.json | jq -r .object.sha) \
  && short_hash=$(echo $hash | cut -c1-5) \