fix(deps): Update plugin com.google.protobuf to v0.9.4 (#6)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| com.google.protobuf | plugin | patch | `0.9.1` -> `0.9.4` |

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build.gradle

@@ -1,6 +1,6 @@
 plugins {
     id 'application'
-    id 'com.google.protobuf' version '0.9.1'
+    id 'com.google.protobuf' version '0.9.4'
     // Generate IntelliJ IDEA's .idea & .iml project files
     id 'idea'
     id "maven-publish"