remove bash requirement in makefile (#6617)

Makefile

@@ -4,7 +4,6 @@ export GO111MODULE=off
 
 GO ?= go
 SED_INPLACE := sed -i
-SHELL ?= bash
 SHASUM ?= shasum -a 256
 
 export PATH := $($(GO) env GOPATH)/bin:$(PATH)
@@ -363,7 +362,7 @@ release-copy:
 
 .PHONY: release-check
 release-check:
-	cd $(DIST)/release/; for file in `find . -type f -name "*"`; do $(SHASUM) $${file:2} > $${file}.sha256; done;
+	cd $(DIST)/release/; for file in `find . -type f -name "*"`; do echo "checksumming $${file}" && $(SHASUM) `echo $${file} | sed 's/^..//'` > $${file}.sha256; done;
 
 .PHONY: release-compress
 release-compress: