Enable stylecheck linter

Add stylecheck linter to golangci-lint.
* Fix style issues.

Signed-off-by: Ben Kochie <superq@gmail.com>

.golangci.yml

@@ -2,6 +2,7 @@ linters:
   enable:
     - misspell
     - revive
+    - stylecheck
   disable:
     # Disable soon to deprecated[1] linters that lead to false
     # positives when build tags disable certain files[2]

collector/cpu_linux.go

@@ -84,7 +84,7 @@ func NewCPUCollector(logger log.Logger) (Collector, error) {
 	isolcpus, err := sysfs.IsolatedCPUs()
 	if err != nil {
 		if !os.IsNotExist(err) {
-			return nil, fmt.Errorf("Unable to get isolated cpus: %w", err)
+			return nil, fmt.Errorf("unable to get isolated cpus: %w", err)
 		}
 		level.Debug(logger).Log("msg", "Could not open isolated file", "error", err)
 	}