cppcheck warning

Author: ngraziano

src/lmic/lmic.us915.h

@@ -85,7 +85,7 @@ class Us915RegionalChannelParams final : public RegionalChannelParams {
   virtual void loadStateWithoutTimeData(RetrieveAbtract &store) final;
 #endif
 
-  Us915RegionalChannelParams(LmicRand &arand);
+  explicit Us915RegionalChannelParams(LmicRand &arand);
 
 private:
   // enabled bits