added android sdk installation instructions to travis config.
added android sdk installation instructions to travis config.

0x1mason/selendroid,SpencerMalone/selendroid,selendroid/selendroid,rasata/selendroid,luohaoyu/selendroid,frolovs/selendroid,selendroid/selendroid,koichirok/selendroid,uchida/selendroid,masbog/selendroid,PrakashGoulla/selendroid,SpencerMalone/selendroid,frolovs/selendroid,lukeis/selendroid,lukeis/selendroid,smiklosovic/selendroid,luohaoyu/selendroid,VikingDen/selendroid,sri096/selendroid,selendroid/selendroid,0x1mason/selendroid,sri096/selendroid,frolovs/selendroid,DominikDary/selendroid,frolovs/selendroid,ghrud92/selendroid,mach6/selendroid,VikingDen/selendroid,lukeis/selendroid,smiklosovic/selendroid,anandsadu/selendroid,asm89/selendroid,koichirok/selendroid,asm89/selendroid,ghrud92/selendroid,frolovs/selendroid,vishals79/appium-uiautomator2-driver,uchida/selendroid,christiannolte/selendroid,uchida/selendroid,rasata/selendroid,smiklosovic/selendroid,asm89/selendroid,sri096/selendroid,PrakashGoulla/selendroid,VikingDen/selendroid,luohaoyu/selendroid,selendroid/selendroid,selendroid/selendroid,DominikDary/selendroid,masbog/selendroid,SpencerMalone/selendroid,PrakashGoulla/selendroid,0x1mason/selendroid,ghrud92/selendroid,ghrud92/selendroid,rasata/selendroid,lukeis/selendroid,vishals79/appium-uiautomator2-driver,smiklosovic/selendroid,mach6/selendroid,sri096/selendroid,anandsadu/selendroid,rasata/selendroid,luohaoyu/selendroid,koichirok/selendroid,asm89/selendroid,appium/selendroid,mach6/selendroid,christiannolte/selendroid,christiannolte/selendroid,smiklosovic/selendroid,luohaoyu/selendroid,DominikDary/selendroid,anandsadu/selendroid,mach6/selendroid,masbog/selendroid,appium/selendroid,vishals79/appium-uiautomator2-driver,0x1mason/selendroid,asm89/selendroid,rasata/selendroid,lukeis/selendroid,VikingDen/selendroid,vishals79/appium-uiautomator2-driver,masbog/selendroid,masbog/selendroid,appium/selendroid,ghrud92/selendroid,uchida/selendroid,mach6/selendroid,SpencerMalone/selendroid,sri096/selendroid,vishals79/appium-uiautomator2-driver,anandsadu/selendroid,uchida/selendroid,PrakashGoulla/selendroid,koichirok/selendroid,SpencerMalone/selendroid,anandsadu/selendroid,christiannolte/selendroid,appium/selendroid,christiannolte/selendroid,appium/selendroid,PrakashGoulla/selendroid,koichirok/selendroid