[MoveTask] Fixed default overwrite behavior.

[siad007]

As seen in the manual - overwrite should be turned on by default.

[codecov]

Codecov Report

Merging #1268 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #1268      +/-   ##
============================================
+ Coverage     51.49%   51.52%   +0.03%     
- Complexity     9320     9321       +1     
============================================
  Files           480      480              
  Lines         22859    22862       +3     
============================================
+ Hits          11771    11780       +9     
+ Misses        11088    11082       -6

Impacted Files	Coverage Δ	Complexity Δ
classes/phing/tasks/system/MoveTask.php	65.04% <100%> (+1.04%)	41 <1> (+1)	⬆️
classes/phing/tasks/system/CopyTask.php	81.19% <0%> (+2.75%)	90% <0%> (ø)	⬇️

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