Syntax highlighting for JSON-LD examples in federation docs

FEDERATION.md

@@ -115,18 +115,20 @@ Allow an actor's signing key to be a separate document, rather than embedded in
 the actor document. In Vervis, the use of that is for server-scope keys (see
 proposal below), but otherwise, an embedded key is just as good.
 
-```
-GET /users/aviva/keys/key1
+`GET /users/aviva/keys/key1`
 
+```json
 { "@context":     "https://w3id.org/security/v1"
 , "@id":          "https://example.dev/users/aviva/keys/key1"
 , "@type":        "Key"
 , "owner":        "https://example.dev/users/aviva"
 , "publicKeyPem": "-----BEGIN PUBLIC KEY----- ..."
 }
+```
 
-GET /users/aviva
+`GET /users/aviva`
 
+```json
 { "@context":
     [ "https://www.w3.org/ns/activitystreams"
     , "https://w3id.org/security/v1"
@@ -165,9 +167,9 @@ document, or a URI specifying the ID of a key defined in a separate document.
 Actors that never need to post activities can simply not specify any keys at
 all.
 
-```
-GET /users/aviva
+`GET /users/aviva`
 
+```json
 { "@context":
     [ "https://www.w3.org/ns/activitystreams"
     , "https://w3id.org/security/v1"