Fix (let default-directory) instead of setq it

The default-directory must be set locally. People setting up Phpactor
while editing will feel that behavior suspiciously. Since let binds
variables only within that block, do not need to kill the buffer.

Author: zonuexe

phpactor.el

@@ -99,8 +99,8 @@
   (let ((package-folder (phpactor--get-package-directory))
         (composer-executable (car (composer--find-executable))))
     (unless composer-executable (error "`composer' not found"))
-    (setq default-directory package-folder)
-    (call-process composer-executable nil (get-buffer-create phpactor--buffer-name) nil "install" "--no-dev")))
+    (let ((default-directory package-folder))
+      (call-process composer-executable nil (get-buffer-create phpactor--buffer-name) nil "install" "--no-dev"))))
 
 (defun phpactor--get-package-directory ()
   "Return the folder where phpactor.el is installed."