Upgrade maven-checkstyle-plugin to 2.17

This patch upgrades maven-checkstyle-plugin to the latest available
version, 2.17.

This is done in order to consume a fix for checkstyle wrongfully
reporting an error if the @return javadoc tag was used in an
annotation type, as it is in Guarded (line 36).

Note that checkstyle has removed the RedundantThrows check (see
discussion at https://github.com/checkstyle/checkstyle/issues/473),
so it was removed from the project's checkstyle.xml configuration.

checkstyle.xml

@@ -36,9 +36,6 @@ limitations under the License.
     <module name="RedundantImport"/>
     <module name="UnusedImports"/>
     <module name="NeedBraces"/>
-    <module name="RedundantThrows">
-      <property name="allowUnchecked" value="true"/>
-    </module>
     <module name="JavadocMethod">
       <property name="allowUndeclaredRTE" value="true"/>
       <property name="scope" value="public" />

pom.xml

@@ -654,7 +654,7 @@
     <plugins>
       <plugin>
         <artifactId>maven-checkstyle-plugin</artifactId>
-        <version>2.15</version>
+        <version>2.17</version>
         <configuration>
           <configLocation>${basedir}/checkstyle.xml</configLocation>
           <enableRulesSummary>false</enableRulesSummary>