Add explicit keyword to 1 arg constructors

The cppcheck tool complains about it otherwise.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Id977a6c349b0b49354b52ac994ea7742e0a39307
diff --git a/control/json/utils/pcie_card_metadata.hpp b/control/json/utils/pcie_card_metadata.hpp
index a879a51..c6b2083 100644
--- a/control/json/utils/pcie_card_metadata.hpp
+++ b/control/json/utils/pcie_card_metadata.hpp
@@ -68,7 +68,7 @@
      *
      * @param[in] systemNames - The system names values
      */
-    PCIeCardMetadata(const std::vector<std::string>& systemNames);
+    explicit PCIeCardMetadata(const std::vector<std::string>& systemNames);
 
     /**
      * @brief Look up a floor index based on a card's metadata