Fix typo in a lexer error message related to line directives.

Author: deadalnix

src/source/dlexer.d

@@ -678,7 +678,7 @@ struct DLexer {
 		import std.format;
 		return getError(
 			t.location,
-			format!"`%s` is not a valis line directive suffix."(
+			format!"`%s` is not a valid line directive suffix."(
 				t.toString(context))
 		);
 

test/invalid/line_directive_suffix.d

@@ -1,4 +1,4 @@
 //T error: line_directive_suffix.d:4:18:
-//T error: `suffix` is not a valis line directive suffix.
+//T error: `suffix` is not a valid line directive suffix.
 
 #line 42 "file.d" suffix