lower min vips version to 8.2

8.2 added vips_bandjoin_const(), which php-vips needs

see #4

Author: jcupitt

ChangeLog

@@ -1,5 +1,9 @@
 vips extension changelog
 
+dev
+---
+	* Lower min vips version to 8.2, see #4
+
 Version 1.0.2 (2016-12-06)
 --------------------------
 	* vips_image_write_to_file() was not setting options, see #3

config.m4

@@ -4,7 +4,8 @@ dnl config.m4 for extension vips
 PHP_ARG_WITH(vips, for vips support,
 [  --with-vips             Include vips support])
 
-VIPS_MIN_VERSION=8.3
+# 8.2 added vips_bandjoin_const(), which php-vips needs
+VIPS_MIN_VERSION=8.2
 
 if test x"$PHP_VIPS" != x"no"; then
   if ! pkg-config --atleast-pkgconfig-version 0.2; then