Remove GWT support.

Also target source 1.9 as we no longer need 1.8 for GWT and hopefully the rest
of the world has moved on from Java 1.8 in the last twenty years.

pom.xml

@@ -41,32 +41,16 @@
     <url>http://github.com/samskivert/jmustache</url>
   </scm>
 
-  <!-- we only uncomment this when checking for plugin updates, due to Maven inanity
   <prerequisites>
-    <maven>3.3.0</maven>
+    <maven>3.9.2</maven>
   </prerequisites>
-  -->
 
   <properties>
-    <source.level>1.8</source.level>
+    <source.level>1.9</source.level>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-    <gwt.version>2.8.2</gwt.version>
-    <gwt.maven.version>2.8.2</gwt.maven.version>
   </properties>
 
   <dependencies>
-    <dependency>
-      <groupId>com.google.gwt</groupId>
-      <artifactId>gwt-dev</artifactId>
-      <version>${gwt.version}</version>
-      <scope>test</scope>
-    </dependency>
-    <dependency>
-      <groupId>com.google.gwt</groupId>
-      <artifactId>gwt-user</artifactId>
-      <version>${gwt.version}</version>
-      <scope>test</scope>
-    </dependency>
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
@@ -82,20 +66,6 @@
   </dependencies>
 
   <build>
-    <resources>
-      <!-- include the source files in our main jar for use by GWT -->
-      <resource>
-        <directory>${project.build.sourceDirectory}</directory>
-        <excludes>
-          <exclude>com/samskivert/mustache/DefaultCollector.java</exclude>
-        </excludes>
-      </resource>
-      <!-- also include the GWT-specific sources -->
-      <resource>
-        <directory>src/main/gwt</directory>
-      </resource>
-    </resources>
-
     <plugins>
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
@@ -104,8 +74,6 @@
         <configuration>
           <source>${source.level}</source>
           <target>${source.level}</target>
-          <testSource>1.8</testSource>
-          <testTarget>1.8</testTarget>
           <fork>true</fork>
           <showDeprecation>true</showDeprecation>
           <showWarnings>true</showWarnings>
@@ -145,7 +113,7 @@
       <plugin>
         <groupId>org.apache.felix</groupId>
         <artifactId>maven-bundle-plugin</artifactId>
-        <version>4.2.0</version>
+        <version>5.1.1</version>
         <extensions>true</extensions>
         <configuration>
           <instructions>
@@ -157,22 +125,6 @@
         </configuration>
       </plugin>
 
-      <plugin>
-        <groupId>org.codehaus.mojo</groupId>
-        <artifactId>gwt-maven-plugin</artifactId>
-        <version>${gwt.maven.version}</version>
-        <executions>
-          <execution>
-            <goals>
-              <goal>test</goal>
-            </goals>
-          </execution>
-        </executions>
-        <configuration>
-          <mode>htmlunit</mode>
-        </configuration>
-      </plugin>
-
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-resources-plugin</artifactId>