Change subtitle color property name to navBarSubtitleColor (#792)

src/deprecated/platformSpecificDeprecated.android.js

     titleBarHidden: originalStyleObject.navBarHidden,
     titleBarHideOnScroll: originalStyleObject.navBarHideOnScroll,
     titleBarTitleColor: processColor(originalStyleObject.navBarTextColor),
-    titleBarSubtitleColor: processColor(originalStyleObject.navBarTextSubtitleColor),
+    titleBarSubtitleColor: processColor(originalStyleObject.navBarSubtitleColor),
     titleBarButtonColor: processColor(originalStyleObject.navBarButtonColor),
     titleBarDisabledButtonColor: processColor(originalStyleObject.titleBarDisabledButtonColor),
     backButtonHidden: originalStyleObject.backButtonHidden,