Set travis versions to 1.5 and 1.6
Set travis versions to 1.5 and 1.6

APTy/cfssl,cloudflare/cfssl,mitchcapper/cfssl,endocode/cfssl,rolandshoemaker/cfssl,rolandshoemaker/cfssl,drcapulet/cfssl,sfurman3/cfssl,endocode/cfssl,cloudflare/cfssl,rolandshoemaker/cfssl,codyli520/cfssl,geligaoli/cfssl,endocode/cfssl,APTy/cfssl,codyli520/cfssl,drcapulet/cfssl,mitchcapper/cfssl,sfurman3/cfssl,APTy/cfssl,codyli520/cfssl,geligaoli/cfssl,sfurman3/cfssl,drcapulet/cfssl,sfurman3/cfssl,geligaoli/cfssl,geligaoli/cfssl,codyli520/cfssl,drcapulet/cfssl,endocode/cfssl,APTy/cfssl,rolandshoemaker/cfssl,cloudflare/cfssl,cloudflare/cfssl,sfurman3/cfssl,rolandshoemaker/cfssl,geligaoli/cfssl,mitchcapper/cfssl,endocode/cfssl,drcapulet/cfssl,codyli520/cfssl,APTy/cfssl