Fix grammar in JSON.stringify tests

test/built-ins/JSON/stringify/15.12.3-0-1.js

@@ -14,7 +14,7 @@ info: |
     This default applies to JSON.stringify, and it must exist as a function
     taking 3 parameters.
 es5id: 15.12.3-0-1
-description: JSON.stringify must exist as be a function
+description: JSON.stringify must exist as a function
 ---*/
 
 var f = JSON.stringify;

test/built-ins/JSON/stringify/15.12.3-0-2.js

@@ -14,7 +14,7 @@ info: |
     This default applies to JSON.stringify, and it must exist as a function
     taking 3 parameters.
 es5id: 15.12.3-0-2
-description: JSON.stringify must exist as be a function taking 3 parameters
+description: JSON.stringify must exist as a function taking 3 parameters
 ---*/
 
 var f = JSON.stringify;

test/built-ins/JSON/stringify/15.12.3_4-1-1.js

@@ -3,7 +3,7 @@
 
 /*---
 es5id: 15.12.3_4-1-1
-description: JSON.stringify a circular object throws a error
+description: JSON.stringify of a circular object throws a TypeError
 ---*/
 
 var obj = {};

test/built-ins/JSON/stringify/15.12.3_4-1-2.js

@@ -3,7 +3,7 @@
 
 /*---
 es5id: 15.12.3_4-1-2
-description: JSON.stringify a indirectly circular object throws a error
+description: JSON.stringify of an indirectly circular object throws a TypeError
 ---*/
 
 var obj = {