Updated the error message in summary page

Author: nbhoski

src/main/resources/com/mathworks/ci/BuildArtifactAction/summary.jelly

@@ -9,7 +9,7 @@
     <p><a href="buildresults">MATLAB Build Results</a></p>
     <span class="${pst.cssClass}">
       <j:if test="${it.totalCount == 0}">
-        <font color="#EF2929"><h5>Unable to generate build artifact. </h5></font>
+        <font color="#EF2929"><h5>Unable to generate a build artifact. </h5></font>
       </j:if>
     </span>
     <p><b>Tasks run: <font color="Blue">${it.totalCount}</font></b></p>