Replace "Login as guest" with "Try the app first" on login page

Fixes vector-im/riot-web#5875

Signed-off-by: Travis Ralston <travpc@gmail.com>

src/components/structures/login/Login.js

@@ -399,7 +399,7 @@ module.exports = React.createClass({
         if (this.props.enableGuest) {
             loginAsGuestJsx =
                 <a className="mx_Login_create" onClick={this._onLoginAsGuestClick} href="#">
-                    { _t('Login as guest') }
+                    { _t('Try the app first') }
                 </a>;
         }