Use Java toolchain with Java 8 for spock module

Author: eddumelendez

modules/spock/build.gradle

@@ -4,6 +4,12 @@ plugins {
 
 description = "Testcontainers :: Spock-Extension"
 
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(8)
+    }
+}
+
 dependencies {
     api project(':testcontainers')
     api 'org.spockframework:spock-core:2.3-groovy-4.0'