Use "comment" for comments in the functions feature

All the other files use "comment" for comments, and the spec in the readme says the key should be "comment".

Author: iconara

tests/functions.json

@@ -572,12 +572,12 @@
       "error": "invalid-arity"
     },
     {
-      "description": "function projection on single arg function",
+      "comment": "function projection on single arg function",
       "expression": "numbers[].to_string(@)",
       "result": ["-1", "3", "4", "5"]
     },
     {
-      "description": "function projection on single arg function",
+      "comment": "function projection on single arg function",
       "expression": "array[].to_number(@)",
       "result": [-1, 3, 4, 5, 100]
     }
@@ -595,7 +595,7 @@
   },
   "cases": [
     {
-      "description": "function projection on variadic function",
+      "comment": "function projection on variadic function",
       "expression": "foo[].not_null(f, e, d, c, b, a)",
       "result": ["b", "c", "d", "e", "f"]
     }
@@ -613,7 +613,7 @@
   },
   "cases": [
     {
-      "description": "sort by field expression",
+      "comment": "sort by field expression",
       "expression": "sort_by(people, &age)",
       "result": [
          {"age": 10, "age_str": "10", "bool": true, "name": 3},
@@ -634,7 +634,7 @@
       ]
     },
     {
-      "description": "sort by function expression",
+      "comment": "sort by function expression",
       "expression": "sort_by(people, &to_number(age_str))",
       "result": [
          {"age": 10, "age_str": "10", "bool": true, "name": 3},
@@ -645,7 +645,7 @@
       ]
     },
     {
-      "description": "function projection on sort_by function",
+      "comment": "function projection on sort_by function",
       "expression": "sort_by(people, &age)[].name",
       "result": [3, "a", "c", "b", "d"]
     },
@@ -733,7 +733,7 @@
   },
   "cases": [
     {
-      "description": "stable sort order",
+      "comment": "stable sort order",
       "expression": "sort_by(people, &age)",
       "result": [
          {"age": 10, "order": "1"},