Adding the `eval` to force variable expansion.

Closes #50
diff --git a/git-flow-release b/git-flow-release
index 08f595b..bb39d52 100644
--- a/git-flow-release
+++ b/git-flow-release
@@ -239,7 +239,7 @@
 			flag sign && opts="$opts -s"
 			[ "$FLAGS_signingkey" != "" ] && opts="$opts -u '$FLAGS_signingkey'"
 			[ "$FLAGS_message" != "" ] && opts="$opts -m '$FLAGS_message'"
-			git tag $opts "$tagname" || \
+			eval git tag $opts "$tagname" || \
 			die "Tagging failed. Please run finish again to retry."
 		fi
 	fi