fix(config): use basename to avoid mixed path separators from glob

[byCedric]

Fixes #2312
Fixes #2326

I noticed glob returning paths with the forward-slash on Windows environments, even though the path.sep correctly returns a backslash. This uses the path.basename to resolve the last folder, regardless of the platform separator.

To outline the issue, here is a log that I used in getProjectName to log the exact output of the projectRoot, sourceRoot, sourceRootParts, path.sep, the bad result (old implementation), and the good result (new implementation):

getProjectName {
  projectRoot: 'C:\\Users\\cedri\\Desktop\\expo-cli\\test-project',
  sourceRoot: 'C:/Users/cedri/Desktop/expo-cli/test-project/ios/testproject',
  sourceRootParts: [ 'C:/Users/cedri/Desktop/expo-cli/test-project/ios/testproject' ],
  resultBad: 'C:/Users/cedri/Desktop/expo-cli/test-project/ios/testproject',
  resultGood: 'testproject',
  pathsep: '\\'
}