title: unable to install web3 in ubuntu 18.04
body: <p>I am installing web3.js in ubuntu 18.04 with the following command:</p>
  
  <pre><code>sudo npm install -g web3
  </code></pre>
  
  <p>and got following error:</p>
  
  <pre><code>&gt; scrypt@6.0.3 preinstall /usr/local/lib/node_modules/web3/node_modules/scrypt
  &gt; node node-scrypt-preinstall.js
  
  Error: Error: Command failed: ./configure
  ./configure: line 1904: config.log: Permission denied
  ./configure: line 1914: config.log: Permission denied
  
  
  &gt; scrypt@6.0.3 install /usr/local/lib/node_modules/web3/node_modules/scrypt
  &gt; node-gyp rebuild
  
  gyp ERR! configure error 
  gyp ERR! stack Error: EACCES: permission denied, mkdir '/usr/local/lib/node_modules/web3/node_modules/scrypt/build'
  gyp ERR! System Linux 4.15.0-45-generic
  gyp ERR! command "/usr/local/bin/node" "/usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "rebuild"
  gyp ERR! cwd /usr/local/lib/node_modules/web3/node_modules/scrypt
  gyp ERR! node -v v10.15.1
  gyp ERR! node-gyp -v v3.8.0
  gyp ERR! not ok 
  npm ERR! code ELIFECYCLE
  npm ERR! errno 1
  npm ERR! scrypt@6.0.3 install: `node-gyp rebuild`
  npm ERR! Exit status 1
  npm ERR! 
  npm ERR! Failed at the scrypt@6.0.3 install script.
  npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
  
  npm ERR! A complete log of this run can be found in:
  npm ERR!     /home/chakshu/.npm/_logs/2019-03-08T15_40_18_402Z-debug.log
  </code></pre>
  
  <p>Although "sudo npm install -g web3@0.20.7" works fine but I want updated web3.js. 
  Please help!</p>