Change the typings of Clock to use a static type as ClassKey

This fixes some compatibility issues with material-ui 4.9.0
It should also be backwards compatible

Fixes mui#1465

lib/src/views/Clock/Clock.tsx

@@ -5,7 +5,9 @@ import ClockType, { ClockViewType } from '../../constants/ClockType';
 import { getHours, getMinutes } from '../../_helpers/time-utils';
 import { withStyles, createStyles, WithStyles, Theme } from '@material-ui/core/styles';
 
-export interface ClockProps extends WithStyles<typeof styles> {
+type ClassKey = 'container' | 'clock' | 'squareMask' | 'pin';
+
+export interface ClockProps extends WithStyles<ClassKey> {
   type: ClockViewType;
   value: number;
   onChange: (value: number, isFinish?: boolean) => void;