Improve language detection

There is a large number of dotenv files out there that do not
actually use a dot in their name. Here is a small comparative study:

- `env`: 2.8k
- `*.env`: | 29.1k
- `?*env`: 12.5k
- `env_*`: 635

For more information on the study, see:
squeak-smalltalk/squeak-app#22 (comment)

package.json

@@ -65,6 +65,12 @@
                     ".env.prod",
                     ".env.prod.local"
                 ],
+                "filenamePatterns": [
+                    "?*env"
+                ],
+                "filenames": [
+                    "env"
+                ],
                 "configuration": "./language-configuration.json"
             }
         ],