编译时，Xcode 7 报错（貌似不影响运行）
While reading /Users/xxx/Development/GitHub/CoreLock/CoreLock/1.png pngcrush caught libpng error:
Not a PNG file..
Could not find file: /Users/xxx/Library/Developer/Xcode/DerivedData/CoreLock-atmjvqzpnuxpdfdfodoemkzmkprc/Build/Products/Debug-iphoneos/CoreLock.app/1.png
Command /Applications/Xcode.app/Contents/Developer/usr/bin/copypng emitted errors but did not return a nonzero exit code to indicate failure
编译时，Xcode 7 报错（貌似不影响运行）
While reading /Users/xxx/Development/GitHub/CoreLock/CoreLock/1.png pngcrush caught libpng error:
Not a PNG file..
Could not find file: /Users/xxx/Library/Developer/Xcode/DerivedData/CoreLock-atmjvqzpnuxpdfdfodoemkzmkprc/Build/Products/Debug-iphoneos/CoreLock.app/1.png
Command /Applications/Xcode.app/Contents/Developer/usr/bin/copypng emitted errors but did not return a nonzero exit code to indicate failure