Obtain official Oracle JDBC driver (#73) (#1899)

Also removed two unnecessary dependencies.

Author: kaiwinter

modules/oracle-xe/build.gradle

@@ -1,17 +1,9 @@
 description = "Testcontainers :: JDBC :: Oracle XE"
 
-repositories {
-    maven {
-        url "https://maven.atlassian.com/3rdparty/"
-    }
-}
-
 dependencies {
     compile project(':jdbc')
 
-    testCompile 'com.oracle:ojdbc6:12.1.0.1-atlassian-hosted'
+    testCompile 'com.oracle.ojdbc:ojdbc8:19.3.0.0'
     testCompile 'com.zaxxer:HikariCP-java6:2.3.8'
     testCompile 'commons-dbutils:commons-dbutils:1.6'
-    testCompile 'org.apache.tomcat:tomcat-jdbc:8.5.4'
-    testCompile 'org.vibur:vibur-dbcp:9.0'
 }