Minor fixes in three error messages

* Fix "can not" -> "cannot" in two messages
* Re-word "Cannot mkdir" to "Cannot create directory"

Change-Id: Ide0cec55eeeebd23bccc136257c80f47638ba858
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties

@@ -84,7 +84,7 @@ cannotListRefs=cannot list refs
 cannotLock=Cannot lock {0}. Ensure that no other process has an open file handle on the lock file {0}.lock, then you may delete the lock file and retry.
 cannotLockPackIn=Cannot lock pack in {0}
 cannotMatchOnEmptyString=Cannot match on empty string.
-cannotMkdirObjectPath=Cannot mkdir {0}/{1}: {2}
+cannotMkdirObjectPath=Cannot create directory {0}/{1}: {2}
 cannotMoveIndexTo=Cannot move index to {0}
 cannotMovePackTo=Cannot move pack to {0}
 cannotOpenService=cannot open {0}