Fix running tree comparison on Chrome

[danieledler]

Chrome blocked scripts loaded over http when served over https

The tree comparison calculation on https://phylo.io fails for me when loaded on Chrome because of this:

Mixed Content: The page at 'https://phylo.io/#' was loaded over HTTPS, but requested an insecure script 'http://peterolson.github.io/BigInteger.js/BigInteger.min.js'. This request has been blocked; the content must be served over HTTPS.

Mixed Content: The page at 'https://phylo.io/#' was loaded over HTTPS, but requested an insecure script 'http://underscorejs.org/underscore-min.js'. This request has been blocked; the content must be served over HTTPS.

treecompare.js:4733 Uncaught ReferenceError: _ is not defined
    at getElementS (treecompare.js:4733)
    at BCN (treecompare.js:4675)
    at getAllBCNs (treecompare.js:4465)
    at getAllBCNs (treecompare.js:4457)
    at getAllBCNs (treecompare.js:4457)
    at getAllBCNs (treecompare.js:4457)
    at getVisibleBCNs (treecompare.js:4470)
    at preprocessTrees (treecompare.js:4610)
    at treecompare.js:4799

Fixes #11