[jvm-packages] upgrade to Scala 2.12 (#4574)

* bump scala to 2.12 which requires java 8 and also newer flink and akka

* put scala version in artifactId

* fix appveyor

* fix for scaladoc issue that looks like https://github.com/scala/bug/issues/10509

* fix ci_build

* update versions in generate_pom.py

* fix generate_pom.py

* apache does not have a download for spark 2.4.3 distro using scala 2.12 yet, so for now i use a tgz i put on s3

* Upload spark-2.4.3-bin-scala2.12-hadoop2.7.tgz to our own S3

* Update Dockerfile.jvm_cross

* Update Dockerfile.jvm_cross

jvm-packages/pom.xml

@@ -5,7 +5,7 @@
     <modelVersion>4.0.0</modelVersion>
 
     <groupId>ml.dmlc</groupId>
-    <artifactId>xgboost-jvm</artifactId>
+    <artifactId>xgboost-jvm_2.12</artifactId>
     <version>0.90</version>
     <packaging>pom</packaging>
     <name>XGBoost JVM Package</name>
@@ -31,12 +31,12 @@
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
-        <maven.compiler.source>1.7</maven.compiler.source>
-        <maven.compiler.target>1.7</maven.compiler.target>
-        <flink.version>1.5.0</flink.version>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+        <flink.version>1.7.2</flink.version>
         <spark.version>2.4.3</spark.version>
-        <scala.version>2.11.12</scala.version>
-        <scala.binary.version>2.11</scala.binary.version>
+        <scala.version>2.12.8</scala.version>
+        <scala.binary.version>2.12</scala.binary.version>
     </properties>
     <repositories>
         <repository>
@@ -372,7 +372,13 @@
         <dependency>
             <groupId>org.scalatest</groupId>
             <artifactId>scalatest_${scala.binary.version}</artifactId>
-            <version>3.0.0</version>
+            <version>3.0.8</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.scalactic</groupId>
+            <artifactId>scalactic_${scala.binary.version}</artifactId>
+            <version>3.0.8</version>
             <scope>test</scope>
         </dependency>
     </dependencies>