Update AppVeyor build configuration

* Update Windows build environment (Visual Studio 2017)
* Add build cache for local Maven repository

appveyor.yml

@@ -1,3 +1,8 @@
+#image: Visual Studio 2017
+environment:
+  JAVA_OPTS: -Xms512m -Xmx2g
+build_script:
+- mvnw.cmd help:evaluate -Dexpression=settings.localRepository
+- mvnw.cmd -B install -Dmaven.test.skip=true -Dmaven.javadoc.skip=true -Dmaven.source.skip=true -Dmaven.deploy.skip=true
 test_script:
-  - mvn package
-build: off
+- mvnw.cmd -B verify -Dmaven.javadoc.skip=true -Dmaven.source.skip=true -Dmaven.deploy.skip=true