Update creating date.

docs/doap_SkyWalking.rdf

@@ -22,7 +22,7 @@
     limitations under the License.
 -->
   <Project rdf:about="http://skywalking.apache.org">
-    <created>2012-04-14</created>
+    <created>2019-04-17</created>
     <license rdf:resource="http://usefulinc.com/doap/licenses/asl20" />
     <name>Apache SkyWalking</name>
     <homepage rdf:resource="http://skywalking.apache.org" />