Change to circuit.measure instead of using the measure function

[antalszava]

Closes #164.

[codecov]

Codecov Report

Merging #191 (a16c6c0) into master (4b39772) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #191   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          292       291    -1     
=========================================
- Hits           292       291    -1     

Impacted Files	Coverage Δ
pennylane_qiskit/qiskit_device.py	100.00% <100.00%> (ø)

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[rmoyard]

Thank you @antalszava for the change, it looks good to me 💯