Fix shell quote on the release task

Author: rafaelfranca

tasks/release.rb

@@ -102,7 +102,7 @@
       abort "[ABORTING] `git status` reports a dirty tree. Make sure all changes are committed"
     end
 
-    unless ENV['SKIP_TAG'] || `git tag | grep '^#{tag}$`.strip.empty?
+    unless ENV['SKIP_TAG'] || `git tag | grep '^#{tag}$'`.strip.empty?
       abort "[ABORTING] `git tag` shows that #{tag} already exists. Has this version already\n"\
             "           been released? Git tagging can be skipped by setting SKIP_TAG=1"
     end