Warning for trailing spaces in folder names

Issue Type: <b>Feature Request</b> My colleague and I had an insanely embarassing and unforgetable experience today at work due to the lack of a feature involving trailing spaces in folder names. I was teaching my colleague how to use Redux with React Native when we got an error in the console. Something along the lines: "Could not resolve module reducers. Path ./reducers not found." I had encountered this issue many times before with previous versions of Expo in which the Metro Bundler cache would not update correctly and it would not recognize the creation of a new folder. I believed the problem to be related to the cache and my colleague and I spent half a day researching the issue on Google and StackOverflow. Eventually, we realized that my colleague had accidentally included a space at the end of the folder name as follows: "reducers ". Not in the import statement, however. There should undoubtedly be a feature in VSCode that enables a warning message by default for trailing spaces in both folder and file names. Though I will admit, the laugh we got out of this was well worth the loss of time. VS Code version: Code - OSS 1.30.2 (61122f88f0bf01e2ac16bdb9e1bc4571755f5bd8, 2019-01-08T23:10:56.746Z) OS version: Linux x64 4.20.6-arch1-1-ARCH <!-- generated by issue reporter -->