Fix error on windows when plug home contains spaces (#154)

Also fixes blank command output.

plug.vim

@@ -1479,7 +1479,7 @@ function! s:update_ruby()
       if iswin
         Timeout::timeout(timeout) do
           tmp = VIM::evaluate('tempname()')
-          system("#{cmd} > #{tmp}")
+          system("(#{cmd}) > #{tmp}")
           data = File.read(tmp).chomp
           File.unlink tmp rescue nil
         end
@@ -1549,7 +1549,7 @@ function! s:update_ruby()
           exists = File.directory? dir
           ok, result =
             if exists
-              dir = esc dir
+              dir = iswin ? dir : esc(dir)
               ret, data = bt.call "#{cd} #{dir} && git rev-parse --abbrev-ref HEAD 2>&1 && git config remote.origin.url", nil, nil, nil
               current_uri = data.lines.to_a.last
               if !ret
@@ -1565,7 +1565,7 @@ function! s:update_ruby()
               else
                 if pull
                   log.call name, 'Updating ...', :update
-                  bt.call "#{cd} #{dir} && (git fetch #{progress} 2>&1 && git checkout -q #{checkout} 2>&1 && git merge --ff-only #{merge} 2>&1 && #{subm})", name, :update, nil
+                  bt.call "#{cd} #{dir} && git fetch #{progress} 2>&1 && git checkout -q #{checkout} 2>&1 && git merge --ff-only #{merge} 2>&1 && #{subm}", name, :update, nil
                 else
                   [true, skip]
                 end
@@ -1618,7 +1618,7 @@ function! s:format_message(bullet, name, message)
 endfunction
 
 function! s:with_cd(cmd, dir)
-  return (s:is_win ? 'cd /d ' : 'cd ').s:esc(a:dir).' && '.a:cmd
+  return printf('cd%s "%s" && %s', s:is_win ? ' /d' : '', escape(a:dir, '"'), a:cmd)
 endfunction
 
 function! s:system(cmd, ...)
@@ -1904,7 +1904,7 @@ function! s:preview_commit()
   execute 'pedit' sha
   wincmd P
   setlocal filetype=git buftype=nofile nobuflisted
-  execute 'silent read !cd' s:esc(g:plugs[name].dir) '&& git show' sha
+  execute 'silent read !cd "'.escape(g:plugs[name].dir, '"').'" && git show' sha
   normal! gg"_dd
   wincmd p
 endfunction
@@ -1966,7 +1966,7 @@ function! s:snapshot(...) abort
   let [type, var, header] = s:is_win ?
     \ ['dosbatch', '%PLUG_HOME%',
     \   ['@echo off', ':: Generated by vim-plug', ':: '.strftime("%c"), '',
-    \    ':: Make sure to PlugUpdate first', '', 'set PLUG_HOME='.s:esc(home)]] :
+    \    ':: Make sure to PlugUpdate first', '', 'set PLUG_HOME='.home]] :
     \ ['sh', '$PLUG_HOME',
     \   ['#!/bin/sh',  '# Generated by vim-plug', '# '.strftime("%c"), '',
     \    'vim +PlugUpdate +qa', '', 'PLUG_HOME='.s:esc(home)]]
@@ -1985,7 +1985,7 @@ function! s:snapshot(...) abort
     let sha = s:system_chomp('git rev-parse --short HEAD', dir)
     if !empty(sha)
       call append(anchor, printf('cd %s && git reset --hard %s',
-            \ substitute(dir, '^'.g:plug_home, var, ''), sha))
+            \ substitute(dir, '^\V'.escape(g:plug_home, '\'), var, ''), sha))
       redraw
     endif
   endfor