SpeechSynthesisTest: check the number of voices against the length of the test data array (VoiceData.voices) instead of hard coding it.

android/eSpeakTests/src/com/reecedunn/espeak/test/SpeechSynthesisTest.java

             final SpeechSynthesis synth = new SpeechSynthesis(getContext(), mCallback);
             mVoices = synth.getAvailableVoices();
             assertThat(mVoices, is(notNullValue()));
-            assertThat(mVoices.size(), is(78));
+            assertThat(mVoices.size(), is(VoiceData.voices.length));
         }
         return mVoices;
     }