iobuild.sh: only install .h files in Headers

cp * -> cp *.h; avoids picking up autoconf files

Change-Id: I57c04562d554431ddf4605af65077f32d90ac58e
diff --git a/iosbuild.sh b/iosbuild.sh
index 306f955..32f2a6d 100755
--- a/iosbuild.sh
+++ b/iosbuild.sh
@@ -109,5 +109,5 @@
   export PATH=${OLDPATH}
 done
 
-cp -a ${SRCDIR}/src/webp/* ${TARGETDIR}/Headers/
+cp -a ${SRCDIR}/src/webp/*.h ${TARGETDIR}/Headers/
 ${LIPO} -create ${LIBLIST} -output ${TARGETDIR}/WebP