camelizeKeys not converting if key starts with upper case letter.

[syntax-e]

Package: "xcase": "^2.0.1"

Repro

camelizeKeys({ Key: 'value' })

Observe result:
{Key: 'value'}

Expected:
{key: 'value'}

This behavior appears to originate here:

xcase/es5/index.js

Line 38 in 8af0a2e

if (isDigit(firstChar) || isUpper(firstChar) || firstChar == separator) {

isUpper(firstChar) causes the method to return without modifying the key and

xcase/es5/index.js

Line 43 in 8af0a2e

if (isUpper(firstChar)) {

never gets a chance to execute.