Fix implicit conversion in string made by numbers.

[corvofeng]

When I passed {hello: '1'}, the hello's value should be a string '1' not a number 1, but code will give this:

------------------------
TESTING:
{ hello: '1' }
OUTPUT:
hello: 1
------------------------

This result isn't I expect, so I make a change.

Signed-off-by: corvofeng corvofeng@gmail.com