makefile: fail semgrep if any check fails (#737)

```bash
$ make semgrep
-- Running inside Docker --
┌─────────────────┐
│ 2 Code Findings │
└─────────────────┘

    command/cp.go
   ❯❯❱ github.err-trailing-whitespaces
	  Trailing whitespace

	   49┆ > s5cmd {{.HelpName}} s3://bucket/prefix/object.gz myobject.gz
	    ⋮┆----------------------------------------
	   50┆

$ echo $?
0
```

Makefile

@@ -55,7 +55,7 @@ unparam:
 
 .PHONY: semgrep
 semgrep: ## Run semgrep
-	@$(semgrep) --quiet --metrics=off --config="r/dgryski.semgrep-go" --config .github/semgrep-rules.yaml .
+	@$(semgrep) --quiet --metrics=off --error --config="r/dgryski.semgrep-go" --config .github/semgrep-rules.yaml .
 
 .PHONY: vet
 vet: