Fix a few cases of "it's" instead of "its" in docs

pkgs/racket-doc/file/scribblings/convertible.scrbl

@@ -31,7 +31,7 @@ should be considered standard:
         and eight numbers; like @racket['png-bytes+bounds], but where
         the image encoded that is in the byte string can be padded in
         each direction (to allow the drawn region to extend beyond
-        it's ``bounding box''), where the extra four numbers in the
+        its ``bounding box''), where the extra four numbers in the
         list specify the amount of padding that was added to the
         image: left, right, top, and bottom}
  @item{@racket['png@2x-bytes] --- like @racket['png-bytes], but for an

pkgs/racket-doc/scribblings/reference/syntax-model.scrbl

@@ -74,7 +74,7 @@ corresponds to the @racket[let] form.
 
 When a @tech{form} parses as the binding of a particular identifier,
 parsing updates a global table that maps a combination of an
-identifier's @tech{symbol} and @tech{scope set} to it's meaning: a
+identifier's @tech{symbol} and @tech{scope set} to its meaning: a
 @tech{variable}, a @tech{syntactic form}, or a @tech{transformer}. An
 identifier refers to a particular binding when the reference's symbol
 and the identifier's symbol are the same, and when the reference's

pkgs/racket-doc/scribblings/reference/syntax.scrbl

@@ -315,7 +315,7 @@ the submodule. In that case, @racket[begin-for-syntax] forms that wrap
 the @racket[module*] form shift the @tech{phase level} of the
 enclosing module's bindings relative to the submodule. The macro
 expander handles such nesting by shifting the @tech{phase level} of
-the @racket[module*] form so that it's body starts at @tech{phase
+the @racket[module*] form so that its body starts at @tech{phase
 level} 0, expanding, and then reverting the @tech{phase level} shift;
 beware that this process can leave @tech{syntax objects} as
 @racket['origin] @tech{syntax property} values out-of-sync with the

pkgs/racket-doc/syntax/scribblings/quote.scrbl

@@ -5,7 +5,7 @@
 @title{Preserving Source Locations}
 
 @defmodule[syntax/quote]{The @racketmodname[syntax/quote] module
-provides support for quoting syntax so that it's source locations
+provides support for quoting syntax so that its source locations
 are preserved in marshaled bytecode form.}
 
 @defform*[[(quote-syntax/keep-srcloc datum)