update treat-err-as-bug test

Author: estebank

src/test/run-make-fulldeps/treat-err-as-bug/Makefile

@@ -2,4 +2,4 @@
 
 all:
 	$(RUSTC) err.rs -Z treat-err-as-bug 2>&1 \
-	    | $(CGREP) "panicked at 'encountered error with \`-Z treat_err_as_bug'"
+	    | $(CGREP) "panicked at 'aborting due to \`-Z treat-err-as-bug=1\`'"