Fix typo in canonical JSON grammar (#1652)

Signed-off-by: Benedykt Błaszkiewicz <tsufeki@gmail.com>

changelogs/appendices/newsfragments/1652.clarification

@@ -0,0 +1 @@
+Fix typo in canonical JSON grammar.

content/appendices.md

@@ -136,12 +136,12 @@ removing insignificant whitespace, fractions, exponents and redundant
 character escapes.
 
     value     = false / null / true / object / array / number / string
-    false     = %x66.61.6c.73.65
+    false     = %x66.61.6C.73.65
-    null      = %x6e.75.6c.6c
+    null      = %x6E.75.6C.6C
     true      = %x74.72.75.65
-    object    = %x7B [ member *( %x2C member ) ] %7D
+    object    = %x7B [ member *( %x2C member ) ] %x7D
     member    = string %x3A value
-    array     = %x5B [ value *( %x2C value ) ] %5B
+    array     = %x5B [ value *( %x2C value ) ] %x5D
     number    = [ %x2D ] int
     int       = %x30 / ( %x31-39 *digit )
     digit     = %x30-39