Fix maven warnings

pom.xml

@@ -10,6 +10,7 @@
 
     <properties>
         <java-version>1.8</java-version>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 
         <scala-library.version>[2.13.0,)</scala-library.version>
 
@@ -73,7 +74,7 @@
         <dependency>
             <groupId>com.google.code.gson</groupId>
             <artifactId>gson</artifactId>
-            <version>LATEST</version>
+            <version>[2.8.5,)</version>
         </dependency>
 
         <dependency>
@@ -89,6 +90,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.8.1</version>
                 <configuration>
                     <source>${java-version}</source>
                     <target>${java-version}</target>