Add support for Whalebrew installed executables

Whalebrew mounts a Docker volume to the host's current working directory (cwd)
therefore the cwd needs to be the temp directory and all file paths which
are to be beautified need to be given to Whalebrew as relative to cwd.
Often this means the temporary directory is simply removed from the prefix
of the file paths, and the cwd = the temporary directory.
See https://github.com/bfirsh/whalebrew#how-it-works for details.

src/beautifiers/executable.coffee

@@ -5,6 +5,7 @@ spawn = require('child_process').spawn
 path = require('path')
 semver = require('semver')
 shellEnv = require('shell-env')
+os = require('os')
 
 parentConfigKey = "atom-beautify.executables"
 
@@ -127,6 +128,7 @@ module.exports = class Executable
     args = _.flatten(args)
     exeName = @cmd
     config = @getConfig()
+    cwd ?= os.tmpDir()
 
     # Resolve executable and all args
     Promise.all([@shellEnv(), Promise.all(args)])
@@ -143,13 +145,17 @@ module.exports = class Executable
       .then(([exeName, args, env, exePath]) =>
         @debug('exePath:', exePath)
         @debug('env:', env)
+        @debug('PATH:', env.PATH)
         @debug('args', args)
+        args = this.relativizePaths(args)
+        @debug('relativized args', args)
 
         exe = exePath ? exeName
         spawnOptions = {
           cwd: cwd
           env: env
         }
+        @debug('spawnOptions', spawnOptions)
 
         @spawn(exe, args, spawnOptions, onStdin)
           .then(({returnCode, stdout, stderr}) =>
@@ -186,6 +192,16 @@ module.exports = class Executable
           )
       )
 
+  relativizePaths: (args) ->
+    tmpDir = os.tmpDir()
+    newArgs = args.map((arg) ->
+      isTmpFile = typeof arg is 'string' and path.isAbsolute(arg) and path.dirname(arg).startsWith(tmpDir)
+      if isTmpFile
+        return path.relative(tmpDir, arg)
+      return arg
+    )
+    newArgs
+
   ###
   Spawn
   ###