Fixed a typo.

plugins/git-extras/git-extras.plugin.zsh

@@ -4,7 +4,7 @@
 #
 #  Completion script for git-extras (http://github.com/tj/git-extras).
 #
-#  This depends on and reueses some of the internals of the _git completion
+#  This depends on and reuses some of the internals of the _git completion
 #  function that ships with zsh itself. It will not work with the _git that ships
 #  with git.
 #