Usage of path.join for adding styles as per suggestions from @fardog

lib/cli.js

@@ -4,6 +4,7 @@ var fs = require('fs')
   , which = require('which')
   , parseArgs = require('minimist')
   , semver = require('semver')
+  , path = require('path')
 
 var PHANTOM_VERSION = "^1.9.0"
 
@@ -110,7 +111,7 @@ cli.prototype.parse = function(argv, next) {
         this.errors.push(err)
       }
     } else {
-      options.css = fs.readFileSync(__dirname + '/../dist/mermaid.css')
+        options.css = fs.readFileSync(path.join(__dirname, '..', 'dist', 'mermaid.css'))
     }
 
     this.checkPhantom = createCheckPhantom(options.phantomPath)