Create temporary directory for javanano test if it does not exist.

The gradle task testNanoGolden fails because the temporary folder it tries to use does not exist.
The task tries to write files to temporaryDir which points to ./compiler/build/tmp/testNanoGolden/ on my machine.
The directory does not exist by default and so the run_nano_test.sh fails.

compiler/build.gradle

@@ -49,6 +49,10 @@ task testGolden(type: Exec, dependsOn: 'generateTestProto') {
 }
 
 task testNanoGolden(type: Exec, dependsOn: 'java_pluginExecutable') {
+  doFirst {
+      temporaryDir.createNewFile();
+  }
+
   environment 'TEST_TMP_DIR', temporaryDir
   commandLine './src/test/run_nano_test.sh'
 }