The in-place version is faster on Julia 0.7 (perhaps also on 0.6). So, update the version.
Reminder, the FFT and friends functions have moved into FFTW package, which forgot to add some exports, so to get your example to work I had to:
Pkg.add("FFTW")
import FFTW: fft, ifft, ifftshift, ifft!
and then the code goes through.