Add Checkstyle SimplifyBooleanExpression

Author: garydgregory

src/conf/checkstyle.xml

@@ -78,6 +78,7 @@ limitations under the License.
     <module name="RedundantImport" />
     <module name="RedundantModifier" />
     <module name="RightCurly" />
+    <module name="SimplifyBooleanExpression" />
     <module name="TypecastParenPad" />    
     <module name="UnusedImports" />
     <module name="UpperEll" />