Fix #355 - PlugSnapshot to create scripts that disable shallow-clone

plug.vim

@@ -2039,10 +2039,10 @@ 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='.home]] :
+    \    ':: Make sure to PlugUpdate first with `let g:plug_shallow = 0`', '', 'set PLUG_HOME='.home]] :
     \ ['sh', '$PLUG_HOME',
     \   ['#!/bin/sh',  '# Generated by vim-plug', '# '.strftime("%c"), '',
-    \    'vim +PlugUpdate +qa', '', 'PLUG_HOME='.s:esc(home)]]
+    \    'vim -c ''let g:plug_shallow = 0 | PlugUpdate | qa''', '', 'PLUG_HOME='.s:esc(home)]]
 
   call s:prepare()
   execute 'setf' type

test/workflow.vader

@@ -1142,7 +1142,7 @@ Execute (PlugSnapshot / #154 issues with paths containing spaces):
   PlugSnapshot
   AssertEqual '#!/bin/sh', getline(1)
   AssertEqual '# Generated by vim-plug', getline(2)
-  AssertEqual 'vim +PlugUpdate +qa', getline(5)
+  AssertEqual 'vim -c ''let g:plug_shallow = 0 | PlugUpdate | qa''', getline(5)
   AssertEqual 'PLUG_HOME=$TMPDIR/plug\ with\ spaces', getline(7)
   AssertEqual 0, stridx(getline(9), 'cd $PLUG_HOME/seoul256.vim/ && git reset --hard')
   AssertEqual 0, stridx(getline(10), 'cd $PLUG_HOME/vim-easy-align/ && git reset --hard')