Update execnet from 1.4.1 to 1.5.0

requirements.txt

 appdirs==1.4.3
 cocos2d==0.6.5
 coverage==4.4.2
-execnet==1.4.1
+execnet==1.5.0
 packaging==16.8
 psutil==5.2.2
 py==1.4.31