Update Jerboa toolchain to v0.2.8

ober

19c49b6e38a364be5b0aa112f801e34b94b29f7c

diff --git a/Makefile b/Makefile
index 790202c..4851d5d 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@
 # crate, so building jerboa-aws needs only jerbuild + a C compiler + cargo.
 # If no jerbuild is found, build/test targets fetch the release toolchain into
 # .jerboa/bin using support/ensure-jerboa.sh.
-JERBOA_VERSION ?= v0.2.3
+JERBOA_VERSION ?= v0.2.8
 JERBOA_TOOL_DIR ?= $(CURDIR)/.jerboa/bin
 JERBUILD ?= $(shell if [ -x ./jerbuild ]; then echo ./jerbuild; \
 	elif [ -x "$(JERBOA_TOOL_DIR)/jerbuild" ]; then echo "$(JERBOA_TOOL_DIR)/jerbuild"; \