Ignore node_modules in globbing

[yhatt]

In the case using the custom engine or functional engine implemented in #42, Marp CLI will try globbing node_modules when specified a project directory through --input-dir or --server option.

So --server option would output ugly logs 🤮

$ marp --server ~/Documents/marp-cli
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/a11y-dark.css (Marpit theme CSS requires @theme meta.)
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/a11y-light.css (Marpit theme CSS requires @theme meta.)
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/agate.css (Marpit theme CSS requires @theme meta.)
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/an-old-hope.css (Marpit theme CSS requires @theme meta.)
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/androidstudio.css (Marpit theme CSS requires @theme meta.)
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/arduino-light.css (Marpit theme CSS requires @theme meta.)
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/arta.css (Marpit theme CSS requires @theme meta.)
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/ascetic.css(Marpit theme CSS requires @theme meta.)
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/atelier-cave-dark.css (Marpit theme CSS requires @theme meta.)
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/atelier-cave-light.css (Marpit theme CSS requires @theme meta.)
[  WARN ] Cannot register theme CSS: ./Documents/marp-cli/node_modules/highlight.js/styles/atelier-dune-dark.css (Marpit theme CSS requires @theme meta.)
...

This PR will ignore node_modules directory in globbing by add a pattern to ignore **/node_modules.

Example

~/Documents/marp-cli/
├── deck-a.md
├── deck-b.md
├── deck-c.md
├── node_modules
├── package-lock.json
└── package.json

Previous behavior

$ ./marp-cli.js ~/Documents/marp-cli/
[  INFO ] Converting 61 markdowns...
...

Fixed behavior

$ ./marp-cli.js ~/Documents/marp-cli/
[  INFO ] Converting 3 markdowns...
...

If you were to convert markdown files included in node_modules, you may specify node_modules directory directly.

Server

node_modules directory would be hidden from the directory index provided by --server option too.

But it still could be accessible to http://localhost:8080/node_modules/.