title: Exception while creating a ProcessEngine with PostgreSQL
body: <p>I’m trying to update the Camunda DMN table programmatically and deploy it again after the update. 
  But while creating a process engine, getting the exception for H2 driver, but for my given project I’m using the PostgreSQL database for Camunda tables.</p>
  
  <pre><code>ProcessEngine processEngine = ProcessEngineConfiguration
                  .createStandaloneInMemProcessEngineConfiguration().buildProcessEngine();
  
  
  org.camunda.bpm.engine.repository.Deployment deployment = processEngine.getRepositoryService()
                      .createDeployment()
                      .addString(fileName, Dmn.convertToString(dmnModelInstance))
                      .name("Deployment after update").deploy();                
  </code></pre>
  
  <p>java.sql.SQLException: Error setting driver on UnpooledDataSource. Cause: java.lang.ClassNotFoundException: org.h2.Driver
      at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.initializeDriver(UnpooledDataSource.java:221)
      at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.doGetConnection(UnpooledDataSource.java:200)
      at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.doGetConnection(UnpooledDataSource.java:196)
      at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.getConnection(UnpooledDataSource.java:93)
      at org.apache.ibatis.datasource.pooled.PooledDataSource.popConnection(PooledDataSource.java:385)
      at org.apache.ibatis.datasource.pooled.PooledDataSource.getConnection(PooledDataSource.java:89)
      at org.camunda.bpm.engine.impl.cfg.ProcessEngineConfigurationImpl.initDatabaseType(ProcessEngineConfigurationImpl.java:1300)</p>