don't use deprecated theme spacing

interface/src/authentication/AuthenticationWrapper.js

@@ -11,7 +11,7 @@ import { withStyles } from '@material-ui/core/styles';
 
 const styles = theme => ({
   loadingPanel: {
-    padding: theme.spacing.unit * 2,
+    padding: theme.spacing(2),
     display: "flex",
     alignItems: "center",
     justifyContent: "center",
@@ -19,7 +19,7 @@ const styles = theme => ({
     flexDirection: "column"
   },
   progress: {
-    margin: theme.spacing.unit * 4,
+    margin: theme.spacing(4),
   }
 });