Fix missing font family for ios in typography

[sanjeevyadavIT]

Describe the bug sans-serif font family is not available in iOS, so app will crash.

Current Behavior App will crash in iOS device

Steps to Reproduce Please provide detailed steps for reproducing the issue.

1. Open typography.js

2. Change these lines

   import colors from './colors';
   
   const fontFamily = 'sans-serif';

3. With these lines

   import { Platform } from 'react-native';
   import colors from './colors';
   
   const fontFamily = Platform.select({ android: 'sans-serif', ios: 'Helvetica' });

Additional context Add any other context about the problem here.

[ishansinghania]

Can i do this?

[sanjeevyadavIT]

Sure :+1:

and please commit message should be in format as described in contributing file

[ishansinghania]

definitely!