title: Issue with setInterval in Nodejs
body: <p>I have this block of code and it's throwing me the following error:</p>
  
  <pre><code>            this.modifyAspect('health');
                   ^
  TypeError: Object #&lt;Timer&gt; has no method 'modifyAspect'
      at Timer.tick (/Users/martinluz/Documents/Nodes/societ/node_modules/societal/societal.js:93:9)
      at Timer.exports.setInterval.timer.ontimeout (timers.js:234:14)
  </code></pre>
  
  <p>I've tried calling <code>modifyAspects()</code> as <code>Societ.modifyAspects</code>, <code>this.modifyAspects()</code> and <code>modifyAspects()</code>, and only got errors. Any help or suggestions are appreciated...</p>
  
  <p>This is the code:</p>
  
  <pre><code>  var Societ = function(inboundConfig){
  
      this.population = undefined;
      this.owner_id =  undefined;
      this.owner_name = undefined;
      this.config = inboundConfig;
      this.aspects = {
          education:{
              facilities: undefined,
              rating: undefined
          },
          health: {
              facilities: undefined,
              rating: undefined
          }
      };
  
      this.modifiers = {
          health: 1,
          education: 2,
          population: 2
      };
  
      this.tickio = function(){
          console.log('tickio');
      }
  
      return{
          config: this.config,
          bootstrap: function(){
              this.owner_id = this.config.owner_id;
              setInterval(this.tick, 10000); /*** Problematic line ***/
          },
          yield: function(){
  
              console.log(this.population);   
          },
          getOwnerId: function(){
              return this.owner_id;
          },
          modifyAspect: function(aspect){
              console.log('Modifying aspect: '+aspect);
          },
          tick: function(){
              console.log('Ticking!');
              this.modifyAspect('health');
              console.log('Recalculate education');
              console.log('Recalculate population');
          },
  
      }
  }
  </code></pre>