gradlew error while setting up the environment

So I was about to start minecraft modding and so installed the forge source , jdk 64 bit and everything needed but when I do the command ".\gradlew tasks" in the powershell I keep getting an error and BUILD FAILED.

Here is the ERROR CODE :

PS C:\Java\minecraftmod\Forge-1.8.9\MinecraftForge-1.8.9> .\gradlew tasks
This mapping 'stable_20' was designed for MC 1.8.8! Use at your own peril.

FAILURE: Build failed with an exception.

* Where:
Build file 'C:\Java\minecraftmod\Forge-1.8.9\MinecraftForge-1.8.9\build.gradle' line: 357

* What went wrong:
A problem occurred evaluating root project 'forge'.
> Cannot run program "git": CreateProcess error=2, The system cannot find the file specified

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

Total time: 18.726 secs
PS C:\Java\minecraftmod\Forge-1.8.9\MinecraftForge-1.8.9>

Anyone knows how this can be solved ?