Fix DateTime namespace in return annotations

The DateTime class should be in the global namespace rather than relative to the current class

Author: robbieaverill

src/Gitonomy/Git/Commit.php

@@ -265,7 +265,7 @@ public function getAuthorEmail()
     /**
      * Returns the authoring date.
      *
-     * @return DateTime A time object
+     * @return \DateTime A time object
      */
     public function getAuthorDate()
     {
@@ -295,7 +295,7 @@ public function getCommitterEmail()
     /**
      * Returns the authoring date.
      *
-     * @return DateTime A time object
+     * @return \DateTime A time object
      */
     public function getCommitterDate()
     {