fix(README): tool => tools

Author: shanejonas

README.md

@@ -1,6 +1,6 @@
-# json-schema.tool playground
+# json-schema.tools playground
 
-json-schema.tool is a playground for `json-schema` using [@etclabscore/json-schema-to-types](https://github.com/etclabscore/json-schema-to-types).
+json-schema.tools is a playground for `json-schema` using [@etclabscore/json-schema-to-types](https://github.com/etclabscore/json-schema-to-types).
 
 
 ![json-schema-playground](https://user-images.githubusercontent.com/364566/75207677-45d63600-572e-11ea-8257-09c1fe4f7534.gif)