Guidelines.md - JSON properties names should be in lowerCamelCase.

[pantafive]

Clarify that the JSON properties names should be in lowerCamelCase.

17.2. Casing

Acronyms SHOULD follow the casing conventions as though they were regular words (e.g. Url).
All identifiers including namespaces, entityTypes, entitySets, properties, actions, functions and enumeration values SHOULD use lowerCamelCase.
HTTP headers are the exception and SHOULD use standard HTTP convention of Capitalized-Hyphenated-Terms.

https://github.com/microsoft/api-guidelines/blob/vNext/Guidelines.md#172-casing