Use /bin/sh instead of /bin/bash (PlugSnapshot)

plug.vim

@@ -1518,7 +1518,7 @@ function! s:snapshot(...) abort
     \   ['@echo off', ':: Generated by vim-plug', ':: '.strftime("%c"), '',
     \    ':: Make sure to PlugUpdate first', '', 'set PLUG_HOME='.s:esc(home)]] :
     \ ['sh', '$PLUG_HOME',
-    \   ['#!/bin/bash',  '# Generated by vim-plug', '# '.strftime("%c"), '',
+    \   ['#!/bin/sh',  '# Generated by vim-plug', '# '.strftime("%c"), '',
     \    'vim +PlugUpdate +qa', '', 'PLUG_HOME='.s:esc(home)]]
 
   call s:prepare()

test/workflow.vader

@@ -1017,7 +1017,7 @@ Execute (PlugSnapshot):
   PlugClean!
   PlugInstall
   PlugSnapshot
-  AssertEqual '#!/bin/bash', getline(1)
+  AssertEqual '#!/bin/sh', getline(1)
   AssertEqual '# Generated by vim-plug', getline(2)
   AssertEqual 'vim +PlugUpdate +qa', getline(5)
   AssertEqual 'PLUG_HOME=$TMPDIR/plugged', getline(7)