Fixed wrong grammar in comment

Author: sarutak

core/src/test/scala/org/apache/spark/deploy/ClientSuite.scala

@@ -39,7 +39,7 @@ class ClientSuite extends FunSuite with Matchers {
     ClientArguments.isValidJarUrl("/missing/a/protocol/jarfile.jar") should be (false)
     ClientArguments.isValidJarUrl("not-even-a-path.jar") should be (false)
 
-    // This URI don't have authority and path.
+    // This URI doesn't have authority and path.
     ClientArguments.isValidJarUrl("hdfs:someHost:1234/jarfile.jar") should be (false)
 
     // Invalid syntax.