Upgrade google-java-format to 1.7 (#45)

Also updates maven-plugin-plugin to 3.5 to fix issue with
'helpmojo' goal after updating google-java-format package.

https://github.com/google/google-java-format/releases/tag/google-java-format-1.7

pom.xml

@@ -81,7 +81,7 @@
         <dependency>
             <groupId>com.google.googlejavaformat</groupId>
             <artifactId>google-java-format</artifactId>
-            <version>1.6</version>
+            <version>1.7</version>
         </dependency>
 
         <dependency>
@@ -121,7 +121,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-plugin-plugin</artifactId>
-                <version>3.4</version>
+                <version>3.5</version>
                 <configuration>
                     <goalPrefix>fmt</goalPrefix>
                     <skipErrorNoDescriptorsFound>true</skipErrorNoDescriptorsFound>