[DOC] Fix markup for `String` (#5984)

* Add missing space for `String#start_with?`.
* Add missing pluses for `String#tr` and
  `Methods for Converting to New String` label.
* Move quote into the tag for `Whitespace in Strings` label.

1 files changed, 1 insertions, 1 deletions

diff --git a/string.c b/string.c
index 83d90ff3a9..84af905deb 100644
--- a/string.c
+++ b/string.c
@@ -7998,7 +7998,7 @@ rb_str_tr_bang(VALUE str, VALUE src, VALUE repl)
  *
  *  - Each occurrence of the first character specified by +selector+
  *    is translated to the first character in +replacements+.
- *  - Each occurrence of the second character specified by selector+
+ *  - Each occurrence of the second character specified by +selector+
  *    is translated to the second character in +replacements+.
  *  - And so on.
  *