fix(helm): Use env to locate bash

Leverage '/usr/bin/env bash` for find bash instead of hardcoding
'/bin/bash' since some *nix OSes have it installed elsewhere.
Signed-off-by: Robert James Hernandez <rob@sarcasticadmin.com>

Makefile

@@ -18,7 +18,7 @@ BINDIR    := $(CURDIR)/bin
 BINARIES  := helm tiller
 
 # Required for globs to work correctly
-SHELL=/bin/bash
+SHELL=/usr/bin/env bash
 
 .PHONY: all
 all: build