Deployment with Bash command

Using this piece of YAML:
```
deploy:
	bash:
		command: 'bundle exec cap production deploy'
```

Will run Capistrano and deploy your app to production.
You can use any other deployment tool instead of Capistrano.

README.md

@@ -210,6 +210,7 @@ Drone currently has these `deploy` and `publish` plugins implemented (more to co
 - [nodejitsu](#docs)
 - [ssh](#docs)
 - [tsuru](#docs)
+- [bash](#docs)
 
 **publish**
 - [Amazon s3](#docs)

pkg/plugin/deploy/bash.go

@@ -0,0 +1,13 @@
+package deploy
+
+import (
+	"github.com/drone/drone/pkg/build/buildfile"
+)
+
+type Bash struct {
+	Command string `yaml:"command,omitempty"`
+}
+
+func (g *Bash) Write(f *buildfile.Buildfile) {
+	f.WriteCmd(g.Command)
+}

pkg/plugin/deploy/deployment.go

@@ -19,6 +19,7 @@ type Deploy struct {
 	Openshift    *Openshift    `yaml:"openshift,omitempty"`
 	SSH          *SSH          `yaml:"ssh,omitempty"`
 	Tsuru        *Tsuru        `yaml:"tsuru,omitempty"`
+	Bash         *Bash         `yaml:"bash,omitempty"`
 }
 
 func (d *Deploy) Write(f *buildfile.Buildfile) {
@@ -55,4 +56,7 @@ func (d *Deploy) Write(f *buildfile.Buildfile) {
 	if d.Tsuru != nil {
 		d.Tsuru.Write(f)
 	}
+	if d.Bash != nil {
+		d.Bash.Write(f)
+	}
 }