Fix null pointer exception when the remote session can not be started

Author: rgonalo

src/main/java/io/appium/java_client/AppiumDriver.java

@@ -34,7 +34,7 @@
 public class AppiumDriver extends RemoteWebDriver implements MobileDriver, ContextAware, FindsByIosUIAutomation,
         FindsByAndroidUIAutomator, FindsByAccessibilityId {
 
-  private final MobileErrorHandler errorHandler = new MobileErrorHandler();
+  private final static MobileErrorHandler errorHandler = new MobileErrorHandler();
 
   public AppiumDriver(URL remoteAddress, Capabilities desiredCapabilities){