don't use deprecated theme spacing

interface/src/components/SectionContent.js

@@ -7,8 +7,8 @@ import Typography from '@material-ui/core/Typography';
 
 const styles = theme => ({
   content: {
-    padding: theme.spacing.unit * 2,
-    margin: theme.spacing.unit * 2,
+    padding: theme.spacing(2),
+    margin: theme.spacing(2),
   }
 });
 

interface/src/components/SnackbarNotification.js

@@ -7,7 +7,7 @@ import CloseIcon from '@material-ui/icons/Close';
 
 const styles = theme => ({
   close: {
-    padding: theme.spacing.unit / 2,
+    padding: theme.spacing(0.5),
   },
 });