Fix wording of auth rule 5.1.1

`state_key` is not a subkey of `content`

content/rooms/fragments/v1-auth-rules.md

@@ -45,7 +45,8 @@ The rules are as follows:
     2.  If sender's domain doesn't matches `state_key`, reject.
     3.  Otherwise, allow.
 5.  If type is `m.room.member`:
-    1.  If no `state_key` key or `membership` key in `content`, reject.
+    1.  If there is no `state_key` property, or no `membership` property in
+        `content`, reject.
     2.  If `membership` is `join`:
         1.  If the only previous event is an `m.room.create` and the
             `state_key` is the creator, allow.

content/rooms/fragments/v3-auth-rules.md

@@ -52,7 +52,8 @@ The complete list of rules, as of room version 3, is as follows:
     2.  If sender's domain doesn't matches `state_key`, reject.
     3.  Otherwise, allow.
 5.  If type is `m.room.member`:
-    1.  If no `state_key` key or `membership` key in `content`, reject.
+    1.  If there is no `state_key` property, or no `membership` property in
+        `content`, reject.
     2.  If `membership` is `join`:
         1.  If the only previous event is an `m.room.create` and the
             `state_key` is the creator, allow.

content/rooms/fragments/v8-auth-rules.md

@@ -49,7 +49,8 @@ The rules are as follows:
    property `m.federate` set to `false`, and the `sender` domain of the event
    does not match the `sender` domain of the create event, reject.
 4.  If type is `m.room.member`:
-    1.  If no `state_key` key or `membership` key in `content`, reject.
+    1.  If there is no `state_key` property, or no `membership` property in
+        `content`, reject.
     2.  If `content` has a `join_authorised_via_users_server`
         key:
         1.  If the event is not validly signed by the homeserver of the user ID denoted

content/rooms/v10.md

@@ -121,7 +121,8 @@ The rules are as follows:
    property `m.federate` set to `false`, and the `sender` domain of the event
    does not match the `sender` domain of the create event, reject.
 4.  If type is `m.room.member`:
-    1.  If no `state_key` key or `membership` key in `content`, reject.
+    1.  If there is no `state_key` property, or no `membership` property in
+        `content`, reject.
     2.  If `content` has a `join_authorised_via_users_server`
         key:
         1.  If the event is not validly signed by the homeserver of the user ID denoted

content/rooms/v6.md

@@ -90,7 +90,8 @@ The rules are as follows:
 3.  If event does not have a `m.room.create` in its `auth_events`,
     reject.
 4.  If type is `m.room.member`:
-    1.  If no `state_key` key or `membership` key in `content`, reject.
+    1.  If there is no `state_key` property, or no `membership` property in
+        `content`, reject.
     2.  If `membership` is `join`:
         1.  If the only previous event is an `m.room.create` and the
             `state_key` is the creator, allow.

content/rooms/v7.md

@@ -76,7 +76,8 @@ The rules are as follows:
 3.  If event does not have a `m.room.create` in its `auth_events`,
     reject.
 4.  If type is `m.room.member`:
-    1.  If no `state_key` key or `membership` key in `content`, reject.
+    1.  If there is no `state_key` property, or no `membership` property in
+        `content`, reject.
     2.  If `membership` is `join`:
         1.  If the only previous event is an `m.room.create` and the
             `state_key` is the creator, allow.