Fix test util and assertion

Author: wkillerud

pkgs/sass_language_services/test/lsp/text_document_test.dart

@@ -134,7 +134,7 @@ klmno
 
       expect(
         document.getText(range: range(0, 0, 0, 5)),
-        equals('asdf'),
+        equals('abcde'),
       );
       expect(
         document.getText(range: range(0, 4, 1, 1)),

pkgs/sass_language_services/test/position_utils.dart

@@ -11,6 +11,6 @@ lsp.Position position(int line, int char) {
 lsp.Range range(int startLine, int startChar, int endLine, int endChar) {
   return lsp.Range(
     start: at(line: startLine, char: startChar),
-    end: at(line: startLine, char: startChar),
+    end: at(line: endLine, char: endChar),
   );
 }