HBASE-14991 Fix the '-feature' warning in scala build (Zhan Zhang)

hbase-spark/pom.xml

@@ -537,6 +537,9 @@
                 <configuration>
                     <charset>${project.build.sourceEncoding}</charset>
                     <scalaVersion>${scala.version}</scalaVersion>
+                    <args>
+                        <arg>-feature</arg>
+                    </args>
                 </configuration>
                 <executions>
                     <execution>

hbase-spark/src/main/scala/org/apache/hadoop/hbase/spark/datasources/HBaseResources.scala

@@ -20,6 +20,7 @@ package org.apache.hadoop.hbase.spark.datasources
 import org.apache.hadoop.hbase.TableName
 import org.apache.hadoop.hbase.client._
 import org.apache.hadoop.hbase.spark.HBaseRelation
+import scala.language.implicitConversions
 
 // Resource and ReferencedResources are defined for extensibility,
 // e.g., consolidate scan and bulkGet in the future work.