title: npm install error included as both a dev and production dependency
body: <pre><code>12915 warn whisper-chat-example@1.0.0 No repository field.
  12916 warn The package web3 is included as both a dev and production dependency.
  12917 verbose type ProcessTerminatedError
  12918 verbose stack ProcessTerminatedError: cancel after 1 retries!
  12918 verbose stack     at Farm.&lt;anonymous&gt; (/usr/local/lib/node_modules/npm/node_modules/worker-farm/lib/farm.js:87:25)
  12918 verbose stack     at Array.forEach (&lt;anonymous&gt;)
  12918 verbose stack     at Farm.&lt;anonymous&gt; (/usr/local/lib/node_modules/npm/node_modules/worker-farm/lib/farm.js:81:36)
  12918 verbose stack     at ontimeout (timers.js:427:11)
  12918 verbose stack     at tryOnTimeout (timers.js:289:5)
  12918 verbose stack     at listOnTimeout (timers.js:252:5)
  12918 verbose stack     at Timer.processTimers (timers.js:212:10)
  12919 verbose cwd /Users/ishansrivastava/Desktop/blocks/Decentralized_Chat
  12920 verbose Darwin 18.0.0
  12921 verbose argv "/usr/local/bin/node" "/usr/local/bin/npm" "install"
  12922 verbose node v10.1.0
  12923 verbose npm  v6.0.1
  12924 error cancel after 1 retries!
  12925 verbose exit [ 1, true ]
  </code></pre>
  
  <p>I don't understand what is wrong. How do I solve this? Is it something related with the line <strong>included as both a dev and production dependency</strong>?</p>
  
  <p>While running <code>npm run dev</code> I get:</p>
  
  <pre><code>sh: cross-env: command not found
  npm ERR! file sh
  npm ERR! code ELIFECYCLE
  npm ERR! errno ENOENT
  npm ERR! syscall spawn
  npm ERR! whisper-chat-example@1.0.0 dev: `cross-env NODE_ENV=development webpack-dev-server --hot`
  npm ERR! spawn ENOENT
  npm ERR!
  npm ERR! Failed at the whisper-chat-example@1.0.0 dev script.
  npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
  </code></pre>