Hey the app you are trying to install requires a certificate to be install the only apps that don't need it are These apps.
Playbox HD
Gridlee
Hipstore
Remote Files
PPSSPP
The loophole called the "Date Trick," found by Dario Sepulveda of the GBA4iOS team, is currently being used in the wild by the makers of emulators like GBA4iOS and SNES emulator since last year, allowing iOS users to downloaded and installed unapproved apps through the built-in Safari browser. Technically, by changing the device's date and time back at least two months on an iPad or iPhone, it is possible to bypass the restrictions on unsigned apps, which allows Apple iOS users to easily run emulators without jailbreaking their devices.
This trick was fixed on iOS 8.1 so no we need certificates to install.