Replace the use of the deprecated 'bootJar' Gradle task, 'mainClassName' property with 'mainClass'.

spring-geode-samples/caching/http-session/spring-geode-samples-caching-httpsession.gradle

@@ -20,7 +20,7 @@ dependencies {
 }
 
 bootJar {
-	mainClassName = 'example.app.caching.session.http.BootGeodeHttpSessionCachingApplication'
+	mainClass = 'example.app.caching.session.http.BootGeodeHttpSessionCachingApplication'
 }
 
 bootRun {

spring-geode-samples/caching/inline-async/spring-geode-samples-caching-inline-async.gradle

@@ -26,7 +26,7 @@ dependencies {
 }
 
 bootJar {
-	mainClassName = 'example.app.caching.inline.BootGeodeAsyncInlineCachingClientApplication'
+	mainClass = 'example.app.caching.inline.BootGeodeAsyncInlineCachingClientApplication'
 }
 
 bootRun {

spring-geode-samples/caching/inline/spring-geode-samples-caching-inline.gradle

@@ -23,7 +23,7 @@ dependencies {
 }
 
 bootJar {
-	mainClassName = 'example.app.caching.inline.BootGeodeInlineCachingApplication'
+	mainClass = 'example.app.caching.inline.BootGeodeInlineCachingApplication'
 }
 
 bootRun {

spring-geode-samples/caching/look-aside/spring-geode-samples-caching-lookaside.gradle

@@ -15,7 +15,7 @@ dependencies {
 }
 
 bootJar {
-	mainClassName = 'example.app.caching.lookaside.BootGeodeLookAsideCachingApplication'
+	mainClass = 'example.app.caching.lookaside.BootGeodeLookAsideCachingApplication'
 }
 
 bootRun {

spring-geode-samples/caching/multi-site/spring-geode-samples-caching-multisite.gradle

@@ -23,5 +23,5 @@ dependencies {
 }
 
 bootJar {
-	mainClassName = 'example.app.caching.multisite.client.BootGeodeMultiSiteCachingClientApplication'
+	mainClass = 'example.app.caching.multisite.client.BootGeodeMultiSiteCachingClientApplication'
 }

spring-geode-samples/caching/near/spring-geode-samples-caching-near.gradle

@@ -24,5 +24,5 @@ dependencies {
 }
 
 bootJar {
-	mainClassName = 'example.app.caching.near.BootGeodeNearCachingClientCacheApplication'
+	mainClass = 'example.app.caching.near.BootGeodeNearCachingClientCacheApplication'
 }