Update hard-coded version to 1.5.0-dev (#3450)

Now that 1.4.0 is out the new target is 1.5.0

(See #2390 and #2988 for more context if needed)

main.go

@@ -21,7 +21,7 @@ import (
 )
 
 // Version holds the current Gitea version
-var Version = "1.4.0-dev"
+var Version = "1.5.0-dev"
 
 // Tags holds the build tags used
 var Tags = ""