feat: add JSON to default watched extensions

Since in a server environment JSON files often contain settings,
nodemon should restart by default when the content of a JSON file is changed.

Closes remy#643

README.md

@@ -128,7 +128,7 @@ Now nodemon will only restart if there are changes in the `./app` or `./libs` di
 
 ## Specifying extension watch list
 
-By default, nodemon looks for files with the `.js`, `.coffee`, and `.litcoffee` extensions. If you use the `--exec` option and monitor `app.py` nodemon will monitor files with the extension of `.py`. However, you can specify your own list with the `-e` (or `--ext`) switch like so:
+By default, nodemon looks for files with the `.js`, `.coffee`, `.litcoffee`, and `.json` extensions. If you use the `--exec` option and monitor `app.py` nodemon will monitor files with the extension of `.py`. However, you can specify your own list with the `-e` (or `--ext`) switch like so:
 
     nodemon -e js,jade
 

lib/config/exec.js

@@ -146,7 +146,7 @@ function exec(nodemonOptions, execMap) {
   if (options.exec === 'coffee') {
     // don't override user specified extension tracking
     if (!options.ext) {
-      extension = 'coffee litcoffee js';
+      extension = 'coffee litcoffee js json';
     }
 
     // because windows can't find 'coffee', it needs the real file 'coffee.cmd'
@@ -184,4 +184,4 @@ function exec(nodemonOptions, execMap) {
   }
 
   return options;
-}
+}