Remove extra prefix in distribution.h

src/distribution.h

@@ -40,7 +40,7 @@ public:
     static std::optional<distribution> parse(const std::string& json_data);
 
     // Public functions
-    std::optional<distro_series> distribution::getSeries(const std::string& name_or_version);
+    std::optional<distro_series> getSeries(const std::string& name_or_version);
 
     // Public member variables
     std::string name;