Fixed broken link to common.lark

docs/json_tutorial.md

@@ -78,7 +78,7 @@ By the way, if you're curious what these terminals signify, they are roughly equ
 
 Lark will accept this, if you really want to complicate your life :)
 
-You can find the original definitions in [common.lark](/lark/grammars/common.lark).
+You can find the original definitions in [common.lark](https://github.com/lark-parser/lark/blob/master/lark/grammars/common.lark).
 They're don't strictly adhere to [json.org](https://json.org/) - but our purpose here is to accept json, not validate it.
 
 Notice that terminals are written in UPPER-CASE, while rules are written in lower-case.