Update json_tutorial.md

docs/json_tutorial.md

@@ -79,7 +79,7 @@ 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](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.
+They 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.
 I'll touch more on the differences between rules and terminals later.