remove hard-coded version number from `composer.json`

composer.json

 {
     "name": "bjornjohansen/wplang",
     "description": "Composer plugin to download translation files from wordpress.org",
-    "version": "0.1.1",
     "license": "GPL-2.0+",
     "type": "composer-plugin",
     "authors": [
@@ -21,4 +20,4 @@
     "extra": {
         "class": "BJ\\Wplang\\Wplang"
     }
-}
\ No newline at end of file
+}