Fix #410 Push empty repositories with recent git versions

Git 2.21 (possibly earlier) changed the output of the error for
empty repos from Couldn't to couldn't. Make the regex case
insensitive.

Author: admorgan

.travis.yml

@@ -1,9 +1,14 @@
-dist: trusty
-sudo: false
-
 # Want 'bash' but 'c' works:
 language: c
 
+matrix:
+  include:
+    - name: "Git 2.21 on Ubuntu Xenial"
+      dist: xenial
+    # === This will need to removed when Travis drops support ===
+    - name: "Git 2.15.1 on Ubuntu Trusty"
+      dist: trusty
+
 script:
 # NOTE: we have to make sure we're on a branch (rather than on a detached HEAD) because tests rely on it.
 - git checkout -b travis-ci-dummy-branch-name

lib/git-subrepo

@@ -581,8 +581,9 @@ subrepo:push() {
     if ! OK; then
       # Check if we are pushing to a new upstream repo (or branch) and just
       # push the commit directly. This is common after a `git subrepo init`:
-      local re="(^|"$'\n'")fatal: Couldn't find remote ref "
-      if [[ $output =~ $re ]]; then
+      # Force to case in
+      local re="(^|"$'\n'")fatal: couldn't find remote ref "
+      if [[ ${output,,} =~ $re ]]; then
         o "Pushing to new upstream: $subrepo_remote ($subrepo_branch)."
         new_upstream=true
       else