Update Jerboa toolchain to v0.2.8

ober

4581735b7d85caf69b94e33e3af51da7f240bdd3

diff --git a/Makefile b/Makefile
index a0d7900..c5efd7e 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),)