Makefile update to write cargo.out and compile against nightly

Makefile

@@ -1,4 +1,5 @@
-CARGO = cargo
+CARGO = cargo +$(TOOLCHAIN)
+TOOLCHAIN = nightly
 
 .PHONY: all bench build check clean doc install publish run test update
 
@@ -8,7 +9,7 @@ bench:
 	@$(CARGO) bench
 
 build:
-	@env TERM=xterm-256color $(CARGO) build --color=always 2>&1
+	@env TERM=xterm-256color $(CARGO) build --color=always 2>&1 && rm -f cargo.out || $(CARGO) build 2> cargo.out
 
 check: build test