Upgrade to Spring Boot 2.1.18.RELEASE.

Author: jxblum

gradle.properties

@@ -5,7 +5,7 @@ mockitoVersion=3.6.0
 multithreadedtcVersion=1.01
 pivotalGemFireVersion=9.5.4
 springVersion=5.1.19.RELEASE
-springBootVersion=2.1.18.BUILD-SNAPSHOT
+springBootVersion=2.1.18.RELEASE
 springDataGemFireVersion=2.1.20.RELEASE
 springDataGeodeVersion=2.1.20.RELEASE
 springDataGeodeTestVersion=0.0.8.RELEASE