Fixes #417: Remove extra files in npm package

[pachewise]

Removing test and config files in npm package. Left plugin files though I am wondering if we need these.

npm pack output:

npm notice 
npm notice 📦  [email protected]
npm notice === Tarball Contents === 
npm notice 10.6kB LICENSE                                                 
npm notice 1.0kB  plugins/bind-dictionary/mousetrap-bind-dictionary.js    
npm notice 254B   plugins/bind-dictionary/mousetrap-bind-dictionary.min.js
npm notice 1.2kB  plugins/global-bind/mousetrap-global-bind.js            
npm notice 297B   plugins/global-bind/mousetrap-global-bind.min.js        
npm notice 779B   plugins/pause/mousetrap-pause.js                        
npm notice 242B   plugins/pause/mousetrap-pause.min.js                    
npm notice 5.5kB  plugins/record/mousetrap-record.js                      
npm notice 808B   plugins/record/mousetrap-record.min.js                  
npm notice 33.9kB mousetrap.js                                            
npm notice 5.0kB  mousetrap.min.js                                        
npm notice 887B   package.json                                            
npm notice 431B   plugins/bind-dictionary/README.md                       
npm notice 552B   plugins/global-bind/README.md                           
npm notice 291B   plugins/pause/README.md                                 
npm notice 563B   plugins/README.md                                       
npm notice 391B   plugins/record/README.md                                
npm notice 3.3kB  README.md                                               
npm notice === Tarball Details === 
npm notice name:          mousetrap                               
npm notice version:       1.6.5                                   
npm notice filename:      mousetrap-1.6.5.tgz                     
npm notice package size:  20.1 kB                                 
npm notice unpacked size: 65.9 kB                                 
npm notice shasum:        636bdb5d74a3efa699ce8c3de50dbe6087997a62
npm notice integrity:     sha512-L0N0BNpAC8kEh[...]jJgncUd/ZTnBg==
npm notice total files:   18                                      
npm notice 
mousetrap-1.6.5.tgz

[pachewise]

Noting I took this config from https://github.com/ccampbell/mousetrap/issues/417#issuecomment-451399736