Bug fix in InjectHelper

UpdateParameterTypes() need to be called in order for newMethodDef to
get a ParameterList. Without doing this SimplifyMacros fails on methods
containing "ldarg" instruction.
https://github.com/0xd4d/dnlib/blob/master/src/DotNet/ParameterList.cs#L158
Merge pull request #11 from UbbeLoL/BugFix

Bug fix in InjectHelper