feat(integrations): add first simple npm integration

Integrations are simple helpers to make integration with existing tools easier.
At basic npm support, the integration will set the version before release to the `package.json`

```yml
integrations:
  npm:
    enabled: true
```

cmd/go-semantic-release/commands/changelog.go

@@ -62,10 +62,6 @@ var changelogCmd = &cobra.Command{
 			return err
 		}
 
-		if err = s.WriteChangeLog(generatedChangelog.Content, file); err != nil {
-			log.Fatal(err)
-		}
-
-		return nil
+		return s.WriteChangeLog(generatedChangelog.Content, file)
 	},
 }

cmd/go-semantic-release/commands/integrations.go

@@ -0,0 +1,62 @@
+package commands
+
+import (
+	"github.com/Nightapes/go-semantic-release/internal/integrations"
+	"github.com/Nightapes/go-semantic-release/pkg/semanticrelease"
+	log "github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+)
+
+func init() {
+	integrationsCmd.Flags().Bool("checks", false, "Check for missing values and envs")
+	integrationsCmd.Flags().StringP("out", "o", "CHANGELOG.md", "Name of the file")
+	rootCmd.AddCommand(integrationsCmd)
+}
+
+var integrationsCmd = &cobra.Command{
+	Use:   "integrations",
+	Short: "Call integrations from config file manual",
+	RunE: func(cmd *cobra.Command, args []string) error {
+		config, err := cmd.Flags().GetString("config")
+		if err != nil {
+			return err
+		}
+
+		repository, err := cmd.Flags().GetString("repository")
+		if err != nil {
+			return err
+		}
+
+		force, err := cmd.Flags().GetBool("no-cache")
+		if err != nil {
+			return err
+		}
+
+		configChecks, err := cmd.Flags().GetBool("checks")
+		if err != nil {
+			return err
+		}
+
+		releaseConfig := readConfig(config)
+
+		s, err := semanticrelease.New(releaseConfig, repository, configChecks)
+		if err != nil {
+			return err
+		}
+
+		provider, err := s.GetCIProvider()
+		if err != nil {
+			return err
+		}
+
+		releaseVersion, err := s.GetNextVersion(provider, force)
+		if err != nil {
+			return err
+		}
+		log.Debugf("Found %d commits till last release", len(releaseVersion.Commits))
+
+		i := integrations.New(&releaseConfig.Integrations, releaseVersion)
+
+		return i.Run()
+	},
+}