Fix inconsistency between security 'scheme' and OAI3 specs.

scheme should be case insensitive
OAI/OpenAPI-Specification#1876
https://tools.ietf.org/html/rfc7235#section-2.1

Author: yfer

src/execute/oas3/build-request.js

@@ -147,13 +147,18 @@ export function applySecurities({request, securities = {}, operation = {}, spec}
           }
         }
         else if (type === 'http') {
-          if (schema.scheme === 'basic') {
+          let scheme = schema.scheme;
+          if (scheme) {
+            scheme = scheme.toLowerCase()
+          }
+
+          if (scheme === 'basic') {
             const {username, password} = value
             const encoded = btoa(`${username}:${password}`)
             result.headers.Authorization = `Basic ${encoded}`
           }
 
-          if (schema.scheme === 'bearer') {
+          if (scheme === 'bearer') {
             result.headers.Authorization = `Bearer ${value}`
           }
         }