Bump Mumble version to 1.4.0

The overlay.mumblelay file is a macOS settins form layout file.
The theme replaces this layout (file).

The settings form contains the version number for a overlay version
comparison/check.
This leaves us with the unfortunate result of a version number in this
theme overwriting layout file.

overlay.mumblelay

@@ -1,5 +1,5 @@
 [overlay]
-version=1.3.0
+version=1.4.0
 alwaysself=false
 sort=1
 y=@Variant(\0\0\0\x87>j\xbcl)