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/modifier.cpp b/control/json/utils/modifier.cpp
index 501a035..91978e7 100644
--- a/control/json/utils/modifier.cpp
+++ b/control/json/utils/modifier.cpp
@@ -93,7 +93,7 @@
  */
 struct MinusOperator : public Modifier::BaseOperator
 {
-    MinusOperator(const json& jsonObj) :
+    explicit MinusOperator(const json& jsonObj) :
         arg(ConfigBase::getJsonValue(jsonObj["value"]))
     {}
 
@@ -162,7 +162,7 @@
  */
 struct LessThanOperator : public Modifier::BaseOperator
 {
-    LessThanOperator(const json& jsonObj)
+    explicit LessThanOperator(const json& jsonObj)
     {
         const auto& valueArray = jsonObj["value"];
         if (!valueArray.is_array())