fix typo (#164)

Co-authored-by: Mike Stephane <mike.stephane.kanyarushatsi@cbc.ca>

README.md

@@ -56,7 +56,7 @@ The above will produce the following string output:
 '{"str":"string","num":0,"obj":{"foo":"foo"},"arr":[1,2,3],"bool":true,"nil":null,"undef":undefined,"inf":Infinity,"date":new Date("2016-04-28T22:02:17.000Z"),"map":new Map([["hello","world"]]),"set":new Set([123,456]),"fn":function echo(arg) { return arg; },"re":new RegExp("([^\\\\s]+)", "g"),"big":BigInt("10")}'
 ```
 
-Note: to produced a beautified string, you can pass an optional second argument to `serialize()` to define the number of spaces to be used for the indentation.
+Note: to produce a beautified string, you can pass an optional second argument to `serialize()` to define the number of spaces to be used for the indentation.
 
 ### Automatic Escaping of HTML Characters