Enable focus varients for outlines by default

Author: reinink

__tests__/fixtures/tailwind-output.css

@@ -3195,6 +3195,10 @@ button,
   outline: 0;
 }
 
+.focus\:outline-none:focus {
+  outline: 0;
+}
+
 .overflow-auto {
   overflow: auto;
 }

defaultConfig.stub.js

@@ -863,7 +863,7 @@ module.exports = {
     minWidth: ['responsive'],
     negativeMargin: ['responsive'],
     opacity: ['responsive'],
-    outline: [],
+    outline: ['focus'],
     overflow: ['responsive'],
     padding: ['responsive'],
     pointerEvents: ['responsive'],