fix(headers): allow content-encoding header to handle case-insensitive values (#5890) (#5892)

lib/adapters/http.js

@@ -471,7 +471,7 @@ export default isHttpAdapterSupported && function httpAdapter(config) {
           delete res.headers['content-encoding'];
         }
 
-        switch (res.headers['content-encoding']) {
+        switch ((res.headers['content-encoding'] || '').toLowerCase()) {
         /*eslint default-case:0*/
         case 'gzip':
         case 'x-gzip':

test/unit/adapters/http.js

@@ -517,6 +517,7 @@ describe('supports http with nodejs', function () {
 
       for (const [typeName, zipped] of Object.entries({
         gzip: gzip(responseBody),
+        GZIP: gzip(responseBody),
         compress: gzip(responseBody),
         deflate: deflate(responseBody),
         'deflate-raw': deflateRaw(responseBody),