Error: lwjgl-platform-2.9.4-nightly-20150209-natives-osx.jar not found

im not a computer kind of person but i have been through the files and i could not find the one that seems to be missing from the file it needs to be in. I've found no fixes anywhere. basically when i click launch it says :
Unable to extract native files.
Error details: No such file or directory
Filename on disk: lwjgl-platform-2.9.4-nightly-20150209-natives-osx.jar
Path: /Users/Lauren/Library/Application Support/minecraft/libraries/org/lwjgl/lwjgl/lwjgl-platform/2.9.4-nightly-20150209/lwjgl-platform-2.9.4-nightly-20150209-natives-osx.jar
Exists: false
ive deleted my minecraft files and re-downloaded the launcher hoping it would download the file that is missing but the same problem occurs.
Please help