Update AmoebaMultipoleForceImpl.cpp

@rmcgibbo and @mpharrigan convinced me I should have just fixed it myself.
Update AmoebaMultipoleForceImpl.h

typo fix
Update AmoebaMultipoleForce.cpp

typo fix
Update AmoebaMultipoleForce.h

typo fix
Update amoebaKernels.h

typo fix
Update AmoebaReferenceKernels.h

typo fix
Merge pull request #619 from schwancr/patch-1

Update AmoebaMultipoleForceImpl.cpp