Use `json` instead of `json5` for syntax highlighting (#2017)

* Use json instead of json5 for syntax highlighting

Chroma, the library used for syntax highlighting in Hugo, does not support JSON5 so those code blocks were not highlighted.
However it supports comments in JSON so they are highlighted correctly in the rendered spec.

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

* Add changelog

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

---------

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

changelogs/client_server/newsfragments/2017.clarification

@@ -0,0 +1 @@
+Use `json` instead of `json5` for syntax highlighting.

content/client-server-api/modules/event_replacements.md

@@ -309,7 +309,7 @@ for re-notifying if the sending client feels a large enough revision was made).
 
 For example, if there is an event mentioning Alice:
 
-```json5
+```json
 {
     "event_id": "$original_event",
     "type": "m.room.message",
@@ -324,7 +324,7 @@ For example, if there is an event mentioning Alice:
 
 And an edit to also mention Bob:
 
-```json5
+```json
 {
   "content": {
     "body": "* Hello Alice & Bob!",

content/client-server-api/modules/rich_replies.md

@@ -31,7 +31,7 @@ the `rel_type` and `event_id` properties of `m.relates_to` become *optional*.
 
 An example reply would be:
 
-```json5
+```json
 {
   "content": {
     "m.relates_to": {
@@ -187,7 +187,7 @@ of the replied to event and any users mentioned in that event. See
 
 An example including mentioning the original sender and other users:
 
-```json5
+```json
 {
   "content": {
     "m.relates_to": {