buffer: use correct name for custom inspect symbol

59714cb introduced the
`util.inspect.custom` symbol, but it was exported as
`customInspectSymbol` by `internal/util.js` and referenced as
`inspectSymbol` by `buffer.js`.

PR-URL: #9289
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/buffer.js

@@ -509,7 +509,7 @@ Buffer.prototype.equals = function equals(b) {
 
 
 // Override how buffers are presented by util.inspect().
-Buffer.prototype[internalUtil.inspectSymbol] = function inspect() {
+Buffer.prototype[internalUtil.customInspectSymbol] = function inspect() {
  var str = '';
  var max = exports.INSPECT_MAX_BYTES;
  if (this.length > 0) {
@@ -519,7 +519,7 @@ Buffer.prototype[internalUtil.inspectSymbol] = function inspect() {
  }
  return '<' + this.constructor.name + ' ' + str + '>';
 };
-Buffer.prototype.inspect = Buffer.prototype[internalUtil.inspectSymbol];
+Buffer.prototype.inspect = Buffer.prototype[internalUtil.customInspectSymbol];
 
 Buffer.prototype.compare = function compare(target,
  start,

test/parallel/test-buffer-inspect.js

@@ -34,3 +34,6 @@ assert.doesNotThrow(function() {
  assert.strictEqual(util.inspect(b), expected);
  assert.strictEqual(util.inspect(s), expected);
 });
+
+b.inspect = undefined;
+assert.strictEqual(util.inspect(b), expected);