Fix typo in gentype

Author: ryyppy

pages/docs/gentype/latest/supported-types.mdx

@@ -117,7 +117,7 @@ In case of mixed named and unnamed arguments, consecutive named arguments form s
 
 Function components are exported and imported exactly like normal functions. For example:
 
-```reaspn
+```reason
 [@genType]
 [@react.component]
 let make = (~name) => React.string(name);