better iiif json

Change "scalefactor" to "scaleFactor", thanks regisrob.

See https://github.com/libvips/libvips/issues/1530

ChangeLog

@@ -1,4 +1,5 @@
 24/1/20 started 8.10.0
+- more conformat iiif output from dzsave [regisrob]
 
 20/6/19 started 8.9.1
 - don't use the new source loaders for new_from_file or new_from_buffer, it

configure.ac

@@ -38,7 +38,7 @@ VIPS_VERSION_STRING=$VIPS_VERSION-`date -u -r ChangeLog`
 #   binary interface changes not backwards compatible?: reset age to 0
 
 LIBRARY_CURRENT=54
-LIBRARY_REVISION=1
+LIBRARY_REVISION=2
 LIBRARY_AGE=12
 
 # patched into include/vips/version.h

libvips/foreign/dzsave.c

@@ -1015,7 +1015,7 @@ write_json( VipsForeignSaveDz *dz )
 	gsf_output_printf( out, 
 		"  \"tiles\": [\n"
 		"    {\n"
-		"      \"scalefactors\": [\n" );
+		"      \"scaleFactors\": [\n" );
 
 	for( i = 0; i < dz->layer->n; i++ ) {
 		gsf_output_printf( out,