fix url_search_params to_string for 5C(\) (#984)

Author: anonrig

include/ada/character_sets-inl.h

@@ -470,7 +470,7 @@ constexpr uint8_t WWW_FORM_URLENCODED_PERCENT_ENCODE[32] = {
     // 50     51     52     53     54     55     56     57
     0x00 | 0x00 | 0x00 | 0x00 | 0x00 | 0x00 | 0x00 | 0x00,
     // 58     59     5A     5B     5C     5D     5E     5F
-    0x00 | 0x00 | 0x00 | 0x08 | 0x00 | 0x20 | 0x40 | 0x00,
+    0x00 | 0x00 | 0x00 | 0x08 | 0x10 | 0x20 | 0x40 | 0x00,
     // 60     61     62     63     64     65     66     67
     0x01 | 0x00 | 0x00 | 0x00 | 0x00 | 0x00 | 0x00 | 0x00,
     // 68     69     6A     6B     6C     6D     6E     6F

tests/url_search_params.cpp

@@ -412,8 +412,9 @@ TEST(url_search_params, test_character_set) {
   // - The userinfo percent-encode set is the path percent-encode set and U+002F
   // (/), U+003A (:), U+003B (;), U+003D (=), U+0040 (@), U+005B ([) to U+005E
   // (^), inclusive, and U+007C (|).
-  std::vector<char> unique_keys = {'/', ':', ';', '=', '@', '[',  ']', '^', '|',
-                                   '$', '&', '+', ',', '!', '\'', ')', '~'};
+  std::vector<char> unique_keys = {'/', ':', ';',  '=', '@', '[',
+                                   ']', '^', '|',  '$', '&', '+',
+                                   ',', '!', '\'', ')', '~', '\\'};
   for (auto& unique_key : unique_keys) {
     auto value = "value" + std::string(1, unique_key);
     search_params.set("key", value);