Add future to requirements.txt
Add future to requirements.txt

Allows deploy to Heroku button to work.
sushmitharaj/sampleapp1,strzyczkowskim/weather,ranjan1110/google-map,o-ali/apiai-qr-webhook-sample,ritz11/weather,PrabhuMMoorthy/apiai-weather-webhook-sample,ChethanDev/fulfillment-webhook-weather-python,Gorgory1/bot-ruby-clima-webhook,bhaskar2500/glassdoor_api,bren10k/surfr,birdphanom/kplus,dialogflow/fulfillment-weather-python,evz9/yahooSample,shahil1993/continent,mayankiitg/YourDocChatBot,skmehra/byd-assistant,alexaarris/playground,dhmodi/virtual_patient_assistant,ganeshsp1/photra,alihamza1214/apiai,dhmodi/virtual_patient_assistant,sjoudi/rta-user-profile,sreeneeth/fulfillment-webhook-weather-python,alexpepperb/spty2,Bhavikshah406/airline_assistant,syrindi/weather777,bhaskar2500/glassdoor_api,csjohnstone/ai-response,DariusHolmgren/apiai-weather-webhook-sample,chanuaran/webhook,bren10k/cryptobot,kuldeepdadhich/fin,Deepak54321/YPriceT,fhakamine/ice-client-webhook,kunjal83/Python-Yahoo-Weather-Webhook,tyrex8/prueba,m-zanchi/apiai-splunk-webhook,krisbell/weather,jzawar/highstreet,CyberBuddies/api.ai-google-search,highstreetfashionsteam/apiai-weather-webhook-sample,bot-rpa/fulfillment-webhook-watson-python,demshinivan/RtBBotResearch,sandipsutariya/myFirstWebHook,saffy/fantastic-octo-spork,higjake/census-bureau,imazhar102/test-my-api-ai,arealdeadone/bot-repo,jhofeloto/situr,abaiskiy/darvis,bzachariah/mobile-phone-github,shgam2/TravelFlan_api_ai,mahoobox/situr3,nevermorethesjake/weather,dhmodi/virtual_patient_assistant,EiSandi/apiaitest