fix the condition of max nodes

[hanzou666]

An equal sign isn't contained in the source code, although vg snarls help is as following:

    -m, --max-nodes N      only compute traversals for snarls with <= N nodes [10]

So, I propose to append an equal sign to the condition of max_nodes.

[cgcloud-jenkins]

Can one of the admins verify this patch?

[ekg]

Jenkins, OK to test.

[adamnovak]

Jenkins, OK to test.

[adamnovak]

(Also @ekg should now be a proper Jenkins admin fro the vg project.)

[cgcloud-jenkins]

Jenkins vg tests complete for PR 1840. View the full report here.

19 tests passed, 0 tests failed and 10 tests skipped in 19689 seconds

Tests produced 2684 warnings. 2684 were for lower-than-expected alignment scores