Add missing dependency org.testcontainers:mongodb

Closes gh-18

Author: rainboyan

examples/grace-mongodb/build.gradle

@@ -16,7 +16,7 @@ dependencies {
     runtimeOnly "org.graceframework.plugins:fields"
 
     testImplementation "org.graceframework:grace-test-support"
-    // testImplementation "org.testcontainers:mongodb:1.19.0"
+    testImplementation "org.testcontainers:mongodb:1.19.8"
 
     testImplementation "org.graceframework.plugins:geb"
     testImplementation "org.seleniumhq.selenium:selenium-remote-driver:$seleniumVersion"