build.gradle: fix building the tests

android/build.gradle

             java.srcDirs = ['src']
             res.srcDirs = ['res']
         }
-        instrumentTest.setRoot('eSpeakTests')
-        instrumentTest {
+        androidTest.setRoot('eSpeakTests')
+        androidTest {
             java.srcDirs = ['eSpeakTests/src']
         }
     }