[HOTFIX] [SQL] Maven test compilation issue

Tests compile in SBT but not Maven.

Author: Andrew Or

sql/core/pom.xml

@@ -41,6 +41,13 @@
       <artifactId>spark-core_${scala.binary.version}</artifactId>
       <version>${project.version}</version>
     </dependency>
+    <dependency>
+      <groupId>org.apache.spark</groupId>
+      <artifactId>spark-core_${scala.binary.version}</artifactId>
+      <version>${project.version}</version>
+      <type>test-jar</type>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>org.apache.spark</groupId>
       <artifactId>spark-catalyst_${scala.binary.version}</artifactId>