Convert field name to camel case for GraphqlInputObjecType

[wangyuesong]

Related with #47

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[coveralls]

Pull Request Test Coverage Report for Build 76

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 41.662%

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Totals
Change from base Build 72:	0.1%
Covered Lines:	802
Relevant Lines:	1925

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💛 - Coveralls

[siderakis]

Thanks for the PR!