Adding this.settings and setting it to null

lib/driver.js

@@ -39,6 +39,8 @@ class BaseDriver extends MobileJsonWireProtocol {
     this.shutdownUnexpectedly = false;
     this.noCommandTimer = null;
     this.shouldValidateCaps = shouldValidateCaps;
+    // settings should be instantiated by implementing drivers
+    this.settings = null;
   }
 
   // we only want subclasses to ever extend the contraints