add_text: 'page' is now a mandatory argument
add_text: 'page' is now a mandatory argument

to fix SyntaxError: non-default argument follows default argument
https://travis-ci.org/wikimedia/pywikibot-core/jobs/31764485#L871

actually, there was no reason for making 'page' optional

Change-Id: I3de824dfd61276a3943b543db5d86f3ba3ce6b28

VcamX/pywikibot-core,magul/pywikibot-core,Darkdadaah/pywikibot-core,h4ck3rm1k3/pywikibot-core,wikimedia/pywikibot-core,npdoty/pywikibot,darthbhyrava/pywikibot-local,trishnaguha/pywikibot-core,magul/pywikibot-core,TridevGuha/pywikibot-core,hasteur/g13bot_tools_new,happy5214/pywikibot-core,valhallasw/pywikibot-core,xZise/pywikibot-core,Darkdadaah/pywikibot-core,icyflame/batman,h4ck3rm1k3/pywikibot-core,wikimedia/pywikibot-core,happy5214/pywikibot-core,emijrp/pywikibot-core,PersianWikipedia/pywikibot-core,jayvdb/pywikibot-core,hasteur/g13bot_tools_new,npdoty/pywikibot,smalyshev/pywikibot-core,hasteur/g13bot_tools_new,jayvdb/pywikibot-core