Fix build issues

- `std::copy_n` requires to #include <algorithm>
- `std::optional` requires C++17 or newer

CMakeLists.txt

@@ -57,7 +57,7 @@ target_link_libraries(i3ipc++
 )
 
 target_compile_options(i3ipc++
-	PRIVATE -std=c++11 -Wall -Wextra -Wno-unused-parameter
+	PRIVATE -std=c++17 -Wall -Wextra -Wno-unused-parameter
 )
 
 target_compile_definitions(i3ipc++

src/ipc-util.cpp

@@ -8,6 +8,7 @@ extern "C" {
 #include <errno.h>
 }
 
+#include <algorithm>
 #include <cstring>
 #include <ios>