doc: assert.deepStrictEqual() description inaccurate

[jmm]

deepStrictEqual() description currently begins with:

Generally identical to assert.deepEqual() with the exception that primitive
values are compared using the strict equality operator ( === ).

But, deepStrictEqual() also compares prototype equality. Example (v5.6.0):

var assert = require("assert");

var a = [0];
var b = {0: 0};

["deepEqual", "deepStrictEqual"].forEach(function (meth) {
  assert[meth](a, b, "not " + meth);
});
// AssertionError: not deepStrictEqual