Remove the dependency on not

The `not` dependency is unused.

Closes #8

Author: remcohaszing

package.json

@@ -47,7 +47,6 @@
     "hast-util-has-property": "^3.0.0",
     "hast-util-to-string": "^3.0.0",
     "hast-util-whitespace": "^3.0.0",
-    "not": "^0.1.0",
     "nth-check": "^2.0.0",
     "property-information": "^6.0.0",
     "space-separated-tokens": "^2.0.0",