Update docs variables

docs/_data/variables/elements/button.json

@@ -14,6 +14,11 @@
       "computed_type": "color",
       "computed_value": "hsl(0, 0%, 100%)"
     },
+    "$button-family": {
+      "name": "$button-family",
+      "value": "false",
+      "type": "boolean"
+    },
     "$button-border-color": {
       "name": "$button-border-color",
       "value": "$grey-lighter",
@@ -158,6 +163,7 @@
   "list": [
     "$button-color",
     "$button-background-color",
+    "$button-family",
     "$button-border-color",
     "$button-border-width",
     "$button-padding-vertical",