Update Yojson ready for OCaml 5

Changes

@@ -7,6 +7,10 @@ o Allow -utf8 with -split-bookmarks -o @B.pdf to produce UTF8 filenames
 o -merge-add-bookmarks now works with unicode filenames
 o Better transformation of some annotation types
 
+Fixes:
+
+o Updated Yojson to remove dependency on Stream, ready for OCaml 5
+
 2.5.1 (January 2022)
 
 o Fix a regression where standard fonts could not be chosen

Makefile

@@ -34,7 +34,8 @@ all : $(TARGETS)
 
 clean ::
 	rm -rf doc foo foo2 out.pdf out2.pdf foo.pdf decomp.pdf *.cmt *.cmti \
-	*.json test/*.pdf debug/*.pdf *.ps *.aux *.idx *.log *.out *.toc *.cut
+	*.json test/*.pdf debug/*.pdf *.ps *.aux *.idx *.log *.out *.toc *.cut \
+	cpdf.top.dSYM
 
 DOC_FILES = cpdfunicodedata.mli cpdferror.mli cpdfdebug.mli cpdfjson.mli \
             cpdfstrftime.mli cpdfcoord.mli cpdfattach.mli cpdfpagespec.mli \