mime: add .json to built-in list of MIME types

Since json is popular and mime package's builtin type does not contain
it, and some Linux distributions do not contain the '/etc/mime.types' file
with minimal installations.

Change-Id: I933393c82be296ef176206c253f4dd19b6f33bb1
GitHub-Last-Rev: ce4eae5
GitHub-Pull-Request: #34737
Reviewed-on: https://go-review.googlesource.com/c/go/+/199657
Run-TryBot: Daniel Martí <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: aisk

src/mime/type.go

@@ -65,6 +65,7 @@ var builtinTypesLower = map[string]string{
 	".jpeg": "image/jpeg",
 	".jpg":  "image/jpeg",
 	".js":   "text/javascript; charset=utf-8",
+	".json": "application/json",
 	".mjs":  "text/javascript; charset=utf-8",
 	".pdf":  "application/pdf",
 	".png":  "image/png",