Fixed some grammar in README.md

[wingeng]

Hi,

Just found some little nits in the README.md.

thanks for an awesome library, looking forward to using it

thanks
wing

[coveralls]

Pull Request Test Coverage Report for Build 17

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 55.459%

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Totals
Change from base Build 15:	0.0%
Covered Lines:	127
Relevant Lines:	229

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💛 - Coveralls

[zhengchun]

Merged, Thanks!