docs: Grammar

Fix a couple cases of using "it's" instead of "its" for the possessive

doc/README.dissector

@@ -3459,7 +3459,7 @@ The arguments to udp_dissect_pdus are:
 
 2.9 PINOs (Protocols in name only)
 
-For the typical dissector there is a 1-1 relationship between it and it's
+For the typical dissector there is a 1-1 relationship between it and its
 protocol. However, there are times when a protocol needs multiple "names"
 because it has multiple dissection functions going into the same dissector
 table. The multiple names removes confusion when picking dissection through

doc/extcap_example.py

@@ -79,7 +79,7 @@ class ArgumentParser(argparse.ArgumentParser):
     def _get_action_from_name(self, name):
         """Given a name, get the Action instance registered with this parser.
         If only it were made available in the ArgumentError object. It is
-        passed as it's first arg...
+        passed as its first arg...
         """
         container = self._actions
         if name is None:

doc/wireshark.adoc

@@ -2586,7 +2586,7 @@ menu:About[Folders]::
 +
 --
 The __Folders__ page lets you view the directory names where Wireshark is
-searching it's various configuration and other files.
+searching its various configuration and other files.
 --
 
 menu:About[Plugins]::