upgrade hadoop to 2.7.1

Author: zhanshaoxiong

pom.xml

@@ -118,7 +118,7 @@
     <sbt.project.name>spark</sbt.project.name>
     <slf4j.version>1.7.16</slf4j.version>
     <log4j.version>1.2.17</log4j.version>
-    <hadoop.version>2.6.5</hadoop.version>
+    <hadoop.version>2.7.1</hadoop.version>
     <protobuf.version>2.5.0</protobuf.version>
     <yarn.version>${hadoop.version}</yarn.version>
     <flume.version>1.6.0</flume.version>