fix value parsing, bump MSRV

clippy.toml

@@ -1,3 +1,3 @@
 # avoid-breaking-exported-api = false # only available on nightly for now
 cognitive-complexity-threshold = 15
-msrv = "1.57.0"
+msrv = "1.64.0"

src/parameters.rs

@@ -180,7 +180,7 @@ pub struct Parameters {
 
 /// Validation function for argument parsing that ensures passed-in extensions are lowercase, and that the user
 /// didn't supply an empty list.
-fn validate_exts(exts: &str) -> Result<(), String> {
+fn validate_exts(exts: &str) -> Result<StringType, String> {
 	// TODO: i would much rather accept uppercase exts and convert them to lowercase than just rejecting lowercase exts...
 
 	if exts.is_empty() {
@@ -190,7 +190,7 @@ fn validate_exts(exts: &str) -> Result<(), String> {
 	if exts.to_lowercase() != exts {
 		return Err(String::from("Supplied extensions must be lowercase"));
 	}
-	Ok(())
+	Ok(exts.into())
 }
 
 /// Further options relating to scanning.