Make Command.Synopsis() implementations one line (#14)

From mitchellh/cli `Command.Synopsis()` is supposed to output a
single line[0], as the `Command.Help()` is used when requesting
detailed help about a specific command. This corrects all the
existing `Synopsis()` implementations.

This fixes #13.

This change also addresses some formatting inconsistencies:
commands are standardized on ending their Help() synopsis
output with a period, but some were missing.

[0]: https://github.com/mitchellh/cli/blob/v1.1.5/command.go#L28-L30

internal/command/plan_output.go

@@ -84,5 +84,5 @@ Options:
 }
 
 func (c *OutputPlanCommand) Synopsis() string {
-	return c.Help()
+	return "Returns the plan details for the provided Plan ID"
 }

internal/command/run_apply.go

@@ -140,5 +140,5 @@ Options:
 }
 
 func (c *ApplyRunCommand) Synopsis() string {
-	return c.Help()
+	return "Applies a run that is paused waiting for confirmation after a plan"
 }

internal/command/run_cancel.go

@@ -135,5 +135,5 @@ Options:
 }
 
 func (c *CancelRunCommand) Synopsis() string {
-	return c.Help()
+	return "Interrupts a run that is currently planning or applying"
 }

internal/command/run_create.go

@@ -133,7 +133,7 @@ func (c *CreateRunCommand) Help() string {
 	helpText := `
 Usage: tfci [global options] run create [options]
 
-	Performs a new plan run in Terraform Cloud, using a configuration version and the workspace's current variables
+	Performs a new plan run in Terraform Cloud, using a configuration version and the workspace's current variables.
 
 Global Options:
 
@@ -157,5 +157,5 @@ Options:
 }
 
 func (c *CreateRunCommand) Synopsis() string {
-	return c.Help()
+	return "Performs a new plan run in Terraform Cloud, using a configuration version and the workspace's current variables"
 }

internal/command/run_discard.go

@@ -123,5 +123,5 @@ Options:
 }
 
 func (c *DiscardRunCommand) Synopsis() string {
-	return c.Help()
+	return "Skips any remaining work on runs that are paused waiting for confirmation or priority"
 }

internal/command/run_show.go

@@ -111,5 +111,5 @@ Options:
 }
 
 func (c *ShowRunCommand) Synopsis() string {
-	return c.Help()
+	return "Returns run details for the provided Terraform Cloud run ID"
 }

internal/command/upload.go

@@ -87,7 +87,7 @@ func (c *UploadConfigurationCommand) Help() string {
 	helpText := `
 Usage: tfci [global options] upload [options]
 
-	Creates and uploads a new configuration version for the provided workspace
+	Creates and uploads a new configuration version for the provided workspace.
 
 Global Options:
 
@@ -109,5 +109,5 @@ Options:
 }
 
 func (c *UploadConfigurationCommand) Synopsis() string {
-	return c.Help()
+	return "Creates and uploads a new configuration version for the provided workspace"
 }