Add more appropriate message when build for iOS on Windows machine

[ageorgieva]

Steps to reproduce:

1. Create project
2. Run $ tns build ios

Actual result:
"ENOENT, no such file or directory 'D:\NS projects\app5\platforms\ios\app5.xcodep
roj\project.pbxproj'" message.

Note: Run $ tns plugin add tns-plugin after this step will show "Cannot read property 'version' of undefined" message.