Update OCaml-call-JS.adoc

Fixing typo.

Author: mirek

site/docsource/OCaml-call-JS.adoc

@@ -1687,7 +1687,7 @@ val tToJs : t -> abs_t
 val tFromJs : abs_t -> t 
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-Note the derived type is slightly different, since `abs_t` is abstrac type, 
+Note the derived type is slightly different, since `abs_t` is abstract type, 
 we assume it is well structured value, so it should always return value of type `t`
  instead of `t option`.