feat(speech-to-text-v1): add missing import

Author: kevinkowa

speech-to-text/src/main/java/com/ibm/watson/speech_to_text/v1/SpeechToText.java

@@ -94,6 +94,7 @@
 import java.util.Map;
 import java.util.Map.Entry;
 import okhttp3.HttpUrl;
+import okhttp3.MultipartBody;
 import okhttp3.OkHttpClient;
 import okhttp3.Request;
 import okhttp3.WebSocket;