Improve linting (#861)

* Disable unused-parameter check due to false positives on Collect()
  calls.
* Enable misspell.
* Simplify error returns.

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

.golangci.yml

@@ -1,6 +1,7 @@
 ---
 linters:
   enable:
+  - misspell
   - revive
 
 issues:
@@ -14,3 +15,9 @@ linters-settings:
     exclude-functions:
       # Never check for logger errors.
       - (github.com/go-kit/log.Logger).Log
+  revive:
+    rules:
+      # https://github.com/mgechev/revive/blob/master/RULES_DESCRIPTIONS.md#unused-parameter
+      - name: unused-parameter
+        severity: warning
+        disabled: true

collector/pg_database.go

@@ -115,10 +115,7 @@ func (c PGDatabaseCollector) Update(ctx context.Context, instance *instance, ch
 			prometheus.GaugeValue, sizeMetric, datname,
 		)
 	}
-	if err := rows.Err(); err != nil {
-		return err
-	}
-	return nil
+	return rows.Err()
 }
 
 func sliceContains(slice []string, s string) bool {

collector/pg_replication_slot.go

@@ -126,8 +126,5 @@ func (PGReplicationSlotCollector) Update(ctx context.Context, instance *instance
 			prometheus.GaugeValue, isActiveValue, slotNameLabel,
 		)
 	}
-	if err := rows.Err(); err != nil {
-		return err
-	}
-	return nil
+	return rows.Err()
 }

collector/pg_statio_user_tables.go

@@ -218,8 +218,5 @@ func (PGStatIOUserTablesCollector) Update(ctx context.Context, instance *instanc
 			datnameLabel, schemanameLabel, relnameLabel,
 		)
 	}
-	if err := rows.Err(); err != nil {
-		return err
-	}
-	return nil
+	return rows.Err()
 }