Upgrade maven-compiler-plugin 3.7.0 -> 3.8.0 (#31)

See:
- https://issues.apache.org/jira/projects/MCOMPILER/versions/12341563
- apache/maven-compiler-plugin@maven-compiler-plugin-3.7.0...maven-compiler-plugin-3.8.0

pom.xml

@@ -414,7 +414,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-compiler-plugin</artifactId>
-                    <version>3.7.0</version>
+                    <version>3.8.0</version>
                     <configuration>
                         <compilerArgs>
                             <!-- XXX: Here, we could pass