Update Jerboa toolchain to v0.2.8

ober

4410670316d014575da7f061f7a3bfa28630f7ea

diff --git a/Makefile b/Makefile
index 960c69e..5476f14 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-JERBOA_VERSION ?= v0.2.3
+JERBOA_VERSION ?= v0.2.8
 JERBOA_TOOL_DIR ?= ../jerboa/dist
 ifeq ($(origin JERBUILD),undefined)
 ifneq ($(wildcard $(JERBOA_TOOL_DIR)/jerbuild),)