util: convert inspect.styles and inspect.colors to prototype-less obj…

…ects

Use a prototype-less object for inspect.styles and inspect.colors to allow
modification of Object.prototype in the REPL.

Fixes: #11614

lib/util.js

@@ -166,7 +166,7 @@ Object.defineProperty(inspect, 'defaultOptions', {
 });
 
 // http://en.wikipedia.org/wiki/ANSI_escape_code#graphics
-inspect.colors = {
+inspect.colors = Object.assign(Object.create(null), {
   'bold': [1, 22],
   'italic': [3, 23],
   'underline': [4, 24],
@@ -180,10 +180,10 @@ inspect.colors = {
   'magenta': [35, 39],
   'red': [31, 39],
   'yellow': [33, 39]
-};
+});
 
 // Don't use 'blue' not visible on cmd.exe
-inspect.styles = {
+inspect.styles = Object.assign(Object.create(null), {
   'special': 'cyan',
   'number': 'yellow',
   'boolean': 'yellow',
@@ -194,7 +194,7 @@ inspect.styles = {
   'date': 'magenta',
   // "name": intentionally not styling
   'regexp': 'red'
-};
+});
 
 const customInspectSymbol = internalUtil.customInspectSymbol;