[port-mapping] Fix typo port_mapping.cpp.

Review: https://reviews.apache.org/r/75042/
diff --git a/src/slave/containerizer/mesos/isolators/network/port_mapping.cpp b/src/slave/containerizer/mesos/isolators/network/port_mapping.cpp
index c5e4e6d..1fd2e22 100644
--- a/src/slave/containerizer/mesos/isolators/network/port_mapping.cpp
+++ b/src/slave/containerizer/mesos/isolators/network/port_mapping.cpp
@@ -5194,7 +5194,7 @@
          << " > /proc/sys/net/ipv4/ip_local_port_range\n";
 
   // Verify that the port range has been updated correctly
-  script << "cat /proc/sys/net/ipv4/ip_local_port_range\n"
+  script << "cat /proc/sys/net/ipv4/ip_local_port_range\n";
 
   // Allow eth0 and lo in the container to accept local packets. We
   // need this because we will set up filters to redirect packets from