Fix Groovy version in INSTALL.txt

This commit uses maven filtering to set the Groovy version rather than an
hard-coded value that can be easily outdated.

Closes gh-6530

spring-boot-cli/src/main/assembly/bin-package.xml

@@ -14,6 +14,20 @@
 			<useDefaultExcludes>true</useDefaultExcludes>
 			<fileMode>644</fileMode>
 			<directoryMode>755</directoryMode>
+			<filtered>true</filtered>
+			<includes>
+				<include>INSTALL.txt</include>
+			</includes>
+		</fileSet>
+		<fileSet>
+			<directory>src/main/content</directory>
+			<outputDirectory>/</outputDirectory>
+			<useDefaultExcludes>true</useDefaultExcludes>
+			<fileMode>644</fileMode>
+			<directoryMode>755</directoryMode>
+			<excludes>
+				<exclude>INSTALL.txt</exclude>
+			</excludes>
 		</fileSet>
 		<fileSet>
 			<directory>src/main/executablecontent</directory>

spring-boot-cli/src/main/content/INSTALL.txt

@@ -7,9 +7,9 @@ in order to complete your installation.
 
 Prerequisites
 -------------
-Spring Boot CLI requires Java JDK v1.6 or above in order to run. Groovy v2.1 is packaged
-as part of this distribution, and therefore does not need to be installed (any existing
-Groovy installation is ignored).
+Spring Boot CLI requires Java JDK v1.6 or above in order to run. Groovy v${groovy.version}
+is packaged as part of this distribution, and therefore does not need to be installed (any
+existing Groovy installation is ignored).
 
 The CLI will use whatever JDK it finds on your path, to check that you have an appropriate
 version you should run: