Move comment in tox.ini due to recent bug in pip
Move comment in tox.ini due to recent bug in pip

As discussed in #1554

* https://bitbucket.org/hpk42/tox/issues/332/
* https://github.com/pypa/pip/issues/3667
flub/pytest,tgoodlet/pytest,jaraco/pytest,nicoddemus/pytest,tareqalayan/pytest,Akasurde/pytest,omarkohl/pytest,alfredodeza/pytest,txomon/pytest,hpk42/pytest,pytest-dev/pytest,RonnyPfannschmidt/pytest,hpk42/pytest,hackebrot/pytest,etataurov/pytest,tomviner/pytest,MichaelAquilina/pytest,eli-b/pytest,skylarjhdownes/pytest,JonathonSonesen/pytest,omarkohl/pytest,rmfitzpatrick/pytest,davidszotten/pytest,The-Compiler/pytest,malinoff/pytest,vodik/pytest,The-Compiler/pytest,ddboline/pytest,vodik/pytest,tomviner/pytest,markshao/pytest,JonathonSonesen/pytest,userzimmermann/pytest,vmalloc/dessert,userzimmermann/pytest,nicoddemus/pytest,pfctdayelise/pytest