Fix percent encoding to not encode digits.

lib/src/percent/encoder.dart

Index: lib/src/percent/encoder.dart
diff --git a/lib/src/percent/encoder.dart b/lib/src/percent/encoder.dart
index c7817609e81c8adc762619d3d7ebd253d4ae7daa..9d05c21c582a5741a823683b8cb03c3d106504f8 100644
--- a/lib/src/percent/encoder.dart
+++ b/lib/src/percent/encoder.dart
@@ -66,7 +66,12 @@ String _convert(List<int> bytes, int start, int end) {
     // exactly `0b100000 = 0x20` less than lowercase letters, so if we ensure
     // that that bit is 1 we ensure that the letter is lowercase.
     var letter = 0x20 | byte;
+    // If the byte is a digit, convert it to its value. All other byte values
+    // are converted to a value greater than 9.
+    // Negative values are detected elsewhere.
+    var digit = 0x30 ^ byte;
     if ((letter >= $a && letter <= $z) ||
+        digit <= 9 ||
         byte == $dash ||
         byte == $dot ||
         byte == $underscore ||