[FIX] Set the http-agent to the form that Rocket.Chat requires for logging (#1482)

Co-authored-by: Diego Mello <diegolmello@gmail.com>

app/utils/fetch.js

 import { Platform } from 'react-native';
 import DeviceInfo from 'react-native-device-info';
 
-export const headers = { 'User-Agent': `RC-RN Mobile/${ DeviceInfo.getVersion() } (build: ${ DeviceInfo.getBuildNumber() }; os: ${ Platform.OS } ${ DeviceInfo.getSystemVersion() })` };
+// this form is required by Rocket.Chat's parser in "app/statistics/server/lib/UAParserCustom.js"
+export const headers = { 'User-Agent': `RC Mobile; ${ Platform.OS } ${ DeviceInfo.getSystemVersion() }; v${ DeviceInfo.getVersion() } (${ DeviceInfo.getBuildNumber() })` };
 
 export default (url, options = {}) => {
 	let customOptions = { ...options, headers };