Enable Stylelint rules for vendor prefixes

This commit also removes a bunch of vendor prefixes that were in the styles
but are no longer needed since PostCSS and Autoprefixer handles generating
them.

src/components/indicators/indicators.scss

@@ -21,7 +21,6 @@
 
 .indicator {
     border-radius: 100em;
-    display: -webkit-flex;
     display: flex;
     align-items: center;
     justify-content: center;
@@ -56,7 +55,6 @@
 
 .countIndicator {
     border-radius: 100em;
-    display: -webkit-flex;
     display: flex;
     align-items: center;
     justify-content: center;
@@ -68,7 +66,6 @@
 
 .playedIndicator {
     border-radius: 100em;
-    display: -webkit-flex;
     display: flex;
     align-items: center;
     justify-content: center;
@@ -80,7 +77,6 @@
 .videoIndicator {
     background: #444;
     border-radius: 100em;
-    display: -webkit-flex;
     display: flex;
     align-items: center;
     justify-content: center;