others --> other's (possessive)

Usage error noted by Grant Griffin <grant.griffin@iowegian.com>.

Doc/lib/libpickle.tex

@@ -386,4 +386,4 @@ The format of the pickle data is identical to that produced using the
 programming language, and there are some freedoms in the encodings of
 certain objects, it's possible that the two modules produce different
 pickled data for the same input objects; however they will always be
-able to read each others pickles back in.)
+able to read each other's pickles back in.)