oci-runtime-tools: fix build with golang 1.16

Add GO111MODULE=auto to GO_PKG_BUILD_VARS to allow the package to be
built in non-module mode.

Module-aware mode will be mandatory in the next golang release.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>

utils/oci-runtime-tools/Makefile

@@ -2,7 +2,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=oci-runtime-tools
 PKG_VERSION:=1.0.0-pre20210122
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 PKG_LICENSE:=Apache-2.0
 PKG_LICENSE_FILES:=LICENSE
 
@@ -54,6 +54,8 @@ define Package/oci-runtime-tests/description
   installable via npm.
 endef
 
+GO_PKG_BUILD_VARS += GO111MODULE=auto
+
 define Build/Compile
 	$(call GoPackage/Build/Compile)
 	$(call GoPackage/Package/Install/Bin,$(PKG_INSTALL_DIR))