franka_hw: Add some missing includes

CHANGELOG.md

 # CHANGELOG
 
+## 0.4.1 - UNRELEASED
+
+Requires `libfranka` >= 0.3.0
+
+  * Added some missing includes to `franka_hw`
+
 ## 0.4.0 - 2018-03-26
 
 Requires `libfranka` >= 0.3.0

franka_hw/include/franka_hw/control_mode.h

@@ -3,6 +3,7 @@
 #pragma once
 
 #include <ostream>
+#include <type_traits>
 
 namespace franka_hw {
 

franka_hw/src/control_mode.cpp

@@ -4,6 +4,7 @@
 
 #include <algorithm>
 #include <iterator>
+#include <string>
 #include <vector>
 
 namespace franka_hw {