title: Min validation not working in Mongoose
body: <p>I have a Schema in which the balance field is declared as shown below</p>
  
  <pre><code>balance: {
      type: Number,
      min: 0,
      default: 30
  }
  </code></pre>
  
  <p>I have set 0 as minimum value so that the balance would not be a negative value. But when I decrement the balance value through update query, balance turns out to be a negative value.</p>
  
  <p>My update query:</p>
  
  <pre><code>User.update({
      _id: mongoose.Types.ObjectId(id)
  }, {
      $inc: {
          balance: -10
      }
  }, function(error, result) {
      // code
  });
  </code></pre>
  
  <p>Did I make any mistake with the code?</p>