Crash on Edge due to use of ES7 "includes" method

[tidoust]

Latest version of ReSpec crashes on Edge while building the list of references with the following error:

TypeError: Object doesn't support property or method 'includes'
   at Anonymous function (https://www.w3.org/Tools/respec/respec-w3c-common:16:2376)
   at Array.prototype.reduce (native code)
   at run (https://www.w3.org/Tools/respec/respec-w3c-common:16:2229)
   at Anonymous function (https://www.w3.org/Tools/respec/respec-w3c-common:10:23241)
   at Promise (native code)
   at Anonymous function (https://www.w3.org/Tools/respec/respec-w3c-common:10:23202)

Problem is Array.prototype.includes is not yet supported in MS Edge.

The function got introduced last week in js/core/biblio.js:
92f8954

(I haven't tested, but I see that it also appears in test/test-build.js where it would probably crash as well)

[marcoscaceres]

Fix released in 3.2.121