sensorcommands: add variant header

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I2d3feee798215f28b444e69f818849b34b42df48
diff --git a/src/sensorcommands.cpp b/src/sensorcommands.cpp
index ce94d5a..d6e6cef 100644
--- a/src/sensorcommands.cpp
+++ b/src/sensorcommands.cpp
@@ -34,6 +34,7 @@
 #include <storagecommands.hpp>
 #include <string>
 #include <utility>
+#include <variant>
 
 namespace ipmi
 {