chore(package): update basichtml to version 0.21.0

Author: greenkeeper[bot]

package.json

@@ -93,7 +93,7 @@
     "@babel/core": "^7.2.2",
     "@babel/preset-env": "^7.2.0",
     "ascjs": "^2.4.0",
-    "basichtml": "^0.20.2",
+    "basichtml": "^0.21.0",
     "coveralls": "^3.0.1",
     "istanbul": "^0.4.5",
     "npm-dollar": "^2.1.2",