100-continue should be case insensitive per rfc 7231

[lambdai]

5.1.1. Expect

The "Expect" header field in a request indicates a certain set of
behaviors (expectations) that need to be supported by the server in
order to properly handle this request. The only such expectation
defined by this specification is 100-continue.

 Expect  = "100-continue"

The Expect field-value is case-insensitive.