Use a single <manifestEntries> element

Previously, there were two <manifestEntries> elements in the CLI's
pom.xml. With certain versions of Maven, this appeared to cause the
first element to be ignored in favour of the second. The problem did
not occur when built locally with Maven 3.1.1, but did occur when built
by Bamboo which, I believe, uses 3.0.x

This commit combines the two <manifestEntries> into one.

spring-boot-cli/pom.xml

@@ -242,8 +242,6 @@
 								</manifest>
 								<manifestEntries>
 									<Start-Class>${start-class}</Start-Class>
-								</manifestEntries>
-								<manifestEntries>
 									<Class-Loader>groovy.lang.GroovyClassLoader</Class-Loader>
 								</manifestEntries>
 							</archive>