Update references of 'master' to 'main'

.travis.yml

@@ -2,8 +2,8 @@ env:
   - BUILD_DOCS=false
 jobs:
   include:
-    - # only build docs on master
-      if: branch = master
+    - # only build docs on main
+      if: branch = main
       env: BUILD_DOCS=true
 
 language: cpp

scripts/update-docs.sh

@@ -1,7 +1,7 @@
 #!/bin/sh -ex
 tuple="$TRAVIS_BRANCH${TRAVIS_TAG:+tag:$TRAVIS_TAG},$TRAVIS_PULL_REQUEST"
 case "$tuple" in
-    dev,false|master,false|tag:*)
+    dev,false|main,false|tag:*)
         ;;
     *)
         exit 0