Fixes Sub-Nav Max-Width

Test Plan: * click views and test subnav width across responsive views

Reviewers: rjmackay, shadowhand

Reviewed By: shadowhand

Subscribers: spaudanjo, sebm90, digitalafrican, eyedol, lkamau, srutto, dkobia

Differential Revision: https://phabricator.ushahidi.com/D410