gradle: bump plugin version to 2.2.0

Also update the dependency declarations since the current ones break
with the new plugin/gradle version.

https://stackoverflow.com/questions/39602587/could-not-get-unknown-property-assemblerelease-for-project

app/build.gradle

@@ -231,14 +231,16 @@ pmd {
     consoleOutput = true
 }
 
-task pmdMain(type: Pmd, dependsOn: assembleDebug) {
+task pmdMain(type: Pmd) {
+    dependsOn 'assembleDebug'
     ruleSetFiles = files("${project.rootDir}/config/pmd/rules.xml", "${project.rootDir}/config/pmd/rules-main.xml")
     ruleSets = [] // otherwise defaults clash with the list in rules.xml
     source 'src/main/java'
     include '**/*.java'
 }
 
-task pmdTest(type: Pmd, dependsOn: assembleDebug) {
+task pmdTest(type: Pmd) {
+    dependsOn 'assembleDebug'
     ruleSetFiles = files("${project.rootDir}/config/pmd/rules.xml", "${project.rootDir}/config/pmd/rules-test.xml")
     ruleSets = [] // otherwise defaults clash with the list in rules.xml
     source 'src/test/java', 'src/androidTest/java'

build.gradle

@@ -3,7 +3,7 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.1.3'
+        classpath 'com.android.tools.build:gradle:2.2.0'
         classpath files('libs/gradle-witness.jar')
     }
 }