Ignore trailing whitespace in commit messages

Because:

* `git` strips trailing whitespace from commit messages, therefore the
  message validation should ignore these as well.

This change:

* Uses `shopt extglob` and bash parameter expansion to avoid adding a
  dependency on `sed` or `tr`, ref:
  http://www.cyberciti.biz/faq/bash-remove-whitespace-from-string/

Notes:

* This is hard to test. Both the `-m` and `-F` `git-commit` args strip
  whitespace before the commit-msg hook is called. The only way I can
  find to persist the trailing whitespace into the commit-msg hook is
  via `nano`, which is difficult to drive with bats.

Fixes #1

Author: tommarshall

hook.sh

@@ -89,8 +89,16 @@ read_commit_msg() {
 
   # read commit message into lines array
   while IFS= read -r; do
+
+    # trim trailing spaces from commit lines
+    shopt -s extglob
+    REPLY="${REPLY%%*( )}"
+    shopt -u extglob
+
+    # ignore comments
     [[ $REPLY =~ ^# ]]
     test $? -eq 0 || COMMIT_MSG_LINES+=("$REPLY")
+
   done < <(cat $COMMIT_MSG_FILE)
 }