Use bash in make bench

Author: vearutop

makefiles/bench.mk

@@ -2,6 +2,7 @@ GO ?= go
 BENCH_COUNT ?= 5
 MASTER_BRANCH ?= master
 REF_NAME ?= $(shell git symbolic-ref -q --short HEAD || git describe --tags --exact-match)
+SHELL := /bin/bash
 
 ## Run benchmark and show result stats, iterations count controlled by BENCH_COUNT, default 5.
 bench: bench-run bench-stat-diff bench-stat