Update version number to 3.5.1.1

php/ext/google/protobuf/package.xml

@@ -13,8 +13,8 @@
  <date>2018-01-05</date>
  <time>11:02:07</time>
  <version>
-  <release>3.5.1</release>
-  <api>3.5.1</api>
+  <release>3.5.1.1</release>
+  <api>3.5.1.1</api>
  </version>
  <stability>
   <release>stable</release>