build: resolve SCHEME from $(JERBOA_HOME)/.chez/bin/scheme

ober

2363ec72736d27035bd8765d569d8e9c49d5d7c5

diff --git a/Makefile b/Makefile
index bf2f28b..8511f3c 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,6 @@
-SCHEME ?= scheme
-JERBOA ?= $(HOME)/mine/jerboa/lib
+JERBOA_HOME ?= $(HOME)/mine/jerboa
+SCHEME ?= $(JERBOA_HOME)/.chez/bin/scheme
+JERBOA ?= $(JERBOA_HOME)/lib
 GHERKIN ?= $(HOME)/mine/gherkin/src
 CHEZHTTPS ?= $(HOME)/mine/chez-https/src
 CHEZSSL ?= $(HOME)/mine/chez-ssl/src
@@ -29,7 +30,7 @@ run-pssm:
 pssm: compile
 	@echo "=== Building pssm alias ==="
 	@echo '#!/bin/sh' > pssm
-	@echo 'exec scheme --libdirs "$(LIBDIRS)" --program "$(CURDIR)/pssm.ss" "$$@"' >> pssm
+	@echo 'exec $(SCHEME) --libdirs "$(LIBDIRS)" --program "$(CURDIR)/pssm.ss" "$$@"' >> pssm
 	@chmod +x pssm
 	@echo "Created ./pssm"