Dependency(deps): Bump antlr4-maven-plugin from 4.2 to 4.9.3

Bumps [antlr4-maven-plugin](https://github.com/antlr/antlr4) from 4.2 to 4.9.3.
- [Release notes](https://github.com/antlr/antlr4/releases)
- [Changelog](https://github.com/antlr/antlr4/blob/master/CHANGES.txt)
- [Commits](https://github.com/antlr/antlr4/compare/4.2...4.9.3)

---
updated-dependencies:
- dependency-name: org.antlr:antlr4-maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

jplag.frontend.java-1.7/pom.xml

@@ -37,7 +37,7 @@
       <plugin>
         <groupId>org.antlr</groupId>
         <artifactId>antlr4-maven-plugin</artifactId>
-        <version>4.2</version>
+        <version>4.9.3</version>
         <executions>
           <execution>
             <goals>

jplag.frontend.python-3/pom.xml

@@ -36,7 +36,7 @@
       <plugin>
         <groupId>org.antlr</groupId>
         <artifactId>antlr4-maven-plugin</artifactId>
-        <version>4.2</version>
+        <version>4.9.3</version>
         <executions>
           <execution>
             <goals>