treewide: Clean up string parameters

Change-Id: I0d3ea6a83465181d3edec1587ff824103489072e
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/config_parser.hpp b/src/config_parser.hpp
index 12ac417..461a22d 100644
--- a/src/config_parser.hpp
+++ b/src/config_parser.hpp
@@ -88,15 +88,15 @@
 
 struct KeyCheck
 {
-    void operator()(const std::string& s);
+    void operator()(std::string_view s);
 };
 struct SectionCheck
 {
-    void operator()(const std::string& s);
+    void operator()(std::string_view s);
 };
 struct ValueCheck
 {
-    void operator()(const std::string& s);
+    void operator()(std::string_view s);
 };
 
 struct string_hash : public std::hash<std::string_view>