Fixes grammar in README.
Fixes grammar in README.

Signed-off-by: Jim Teeuwen <ecb7a7d06775fdaa322142445fc578a45387c607@gmail.com>

jmptrader/go-duktape,olebedev/go-duktape,fattenap/go-duktape,fattenap/go-duktape,mosolovsa/go-duktape,ivan4th/go-duktape,jmptrader/go-duktape,ivan4th/go-duktape