build: #846 Upgrade: string_scanner

pubspec.yaml

@@ -55,7 +55,7 @@ dependencies:
   # For useful log
   logger: ^1.3.0
   # For syntax codes in markdown.
-  string_scanner: ^1.1.1
+  string_scanner: ^1.2.0
   flutter_highlighter: ^0.1.1
   # For finds url from text
   linkify: ^4.1.0