title: Bug in OpenAPI generator? Wrong format for the example value of date datatype
body: <p>I'm using a openapi-generator-maven-plugin with 4.2.3 version.</p>
  
  <p>My configuration looks like this:</p>
  
  <pre><code>                       &lt;typeMappings&gt;
                              &lt;typeMapping&gt;OffsetDate=LocalDate&lt;/typeMapping&gt;
                              &lt;typeMapping&gt;OffsetDateTime=LocalDateTime&lt;/typeMapping&gt;
                          &lt;/typeMappings&gt;
                          &lt;importMappings&gt;
                              &lt;importMapping&gt;java.time.OffsetDate=java.time.LocalDate&lt;/importMapping&gt;
                              &lt;importMapping&gt;java.time.OffsetDateTime=java.time.LocalDateTime&lt;/importMapping&gt;
                          &lt;/importMappings&gt;
                          &lt;!-- pass any necessary config options --&gt;
                          &lt;configOptions&gt;
                              &lt;java8&gt;true&lt;/java8&gt;
                              &lt;skipDefaultInterface&gt;true&lt;/skipDefaultInterface&gt;
                              &lt;dateLibrary&gt;java8&lt;/dateLibrary&gt;
                              &lt;interfaceOnly&gt;true&lt;/interfaceOnly&gt;
                              &lt;swaggerDocketConfig&gt;false&lt;/swaggerDocketConfig&gt;
                              &lt;hateoas&gt;true&lt;/hateoas&gt;
                          &lt;/configOptions&gt;
  </code></pre>
  
  <p>In ma yaml I defined my property with example parameter:</p>
  
  <pre><code> myDate:
     type: "string"
     format: "date"
     description: "My date"
     example: "2012-10-11"
  </code></pre>
  
  <p>But example is ignored by plugin: In my generated code I have:</p>
  
  <pre><code>  @ApiModelProperty(example = "Thu Oct 11 02:00:00 CEST 2012", required = true, value = "My date")
  </code></pre>
  
  <p>I would like have a example like in my yaml file. In YYYY-MM-DD format.</p>
  
  <p>I'm using:</p>
  
  <blockquote>
  <pre><code>    &lt;dependency&gt;
          &lt;groupId&gt;io.springfox&lt;/groupId&gt;
          &lt;artifactId&gt;springfox-swagger2&lt;/artifactId&gt;
          &lt;version&gt;3.0.0-SNAPSHOT&lt;/version&gt;
      &lt;/dependency&gt;
      &lt;dependency&gt;
          &lt;groupId&gt;io.springfox&lt;/groupId&gt;
          &lt;artifactId&gt;springfox-swagger-ui&lt;/artifactId&gt;
          &lt;version&gt;3.0.0-SNAPSHOT&lt;/version&gt;
      &lt;/dependency&gt;
      &lt;dependency&gt;
          &lt;groupId&gt;io.springfox&lt;/groupId&gt;
          &lt;artifactId&gt;springfox-spring-webmvc&lt;/artifactId&gt;
          &lt;version&gt;3.0.0-SNAPSHOT&lt;/version&gt;
      &lt;/dependency&gt;
      &lt;dependency&gt;
          &lt;groupId&gt;org.openapitools&lt;/groupId&gt;
          &lt;artifactId&gt;jackson-databind-nullable&lt;/artifactId&gt;
          &lt;version&gt;0.1.0&lt;/version&gt;
      &lt;/dependency&gt;
      &lt;dependency&gt;
          &lt;groupId&gt;com.fasterxml.jackson.dataformat&lt;/groupId&gt;
          &lt;artifactId&gt;jackson-dataformat-xml&lt;/artifactId&gt;
          &lt;version&gt;2.10.2&lt;/version&gt;
      &lt;/dependency&gt;
  </code></pre>
  </blockquote>