Util: Pass string by const reference

src/util/shell.cpp

@@ -10,7 +10,7 @@ Shell::Shell()
 {
 }
 
-Shell::Shell(std::string output, int status)
+Shell::Shell(const std::string& output, int status)
 	: m_output(output)
 	, m_status(status)
 {

src/util/shell.h

@@ -19,7 +19,7 @@ public:
 	int status() const { return m_status; }
 
 private:
-	Shell(std::string output, int status);
+	Shell(const std::string& output, int status);
 
 	std::string m_output;
 	int m_status { 0 };