Fix issue #88

msfvenom updated and chanegd the output of c shellcode.  Adding the flag
-f and a lower c outputs the correct data.  We need to remove the first
18 char instead of 4 now.  Not sure why an error gets thrown but it
doesn't affect anything so I just threw it to /dev/null
Merge pull request #103 from b00stfr3ak/msfvenom_issue

Fix issue #88