Fix restart command in neovim when terminal in use

Neovim doesn't allow you to replace a terminal buffer if the buffer has
received some output, so we tell it that the buffer is not modified as a
hackaround.

Fixes #154

autoload/vimspector/internal/neoterm.vim

@@ -60,6 +60,7 @@ function! vimspector#internal#neoterm#Start( cmd, opts ) abort
   try
     let old_env = vimspector#internal#neoterm#PrepareEnvironment(
           \ a:opts[ 'env' ] )
+    setlocal nomodified
     let id = termopen( a:cmd, {
           \ 'cwd': a:opts[ 'cwd' ],
           \ 'env': a:opts[ 'env' ],