Fixed echo of cursor after input is finished. (fixes manifoldco#117)

Based on: manifoldco#118 by github.com/richardmcsong,
taking only the changes required to fix issue manifoldco#117.

Author: jamesdobson

cursor.go

@@ -1,6 +1,9 @@
 package promptui
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 // Pointer is A specific type that translates a given set of runes into a given
 // set of runes pointed at by the cursor.
@@ -144,6 +147,11 @@ func (c *Cursor) Get() string {
 	return string(c.input)
 }
 
+// GetMask returns a mask string with length equal to the input
+func (c *Cursor) GetMask(mask rune) string {
+	return strings.Repeat(string(mask), len(c.input))
+}
+
 // Replace replaces the previous input with whatever is specified, and moves the
 // cursor to the end position
 func (c *Cursor) Replace(input string) {

prompt.go

@@ -218,9 +218,9 @@ func (p *Prompt) Run() (string, error) {
 		return "", err
 	}
 
-	echo := cur.Format()
+	echo := cur.Get()
 	if p.Mask != 0 {
-		echo = cur.FormatMask(p.Mask)
+		echo = cur.GetMask(p.Mask)
 	}
 
 	prompt := render(p.Templates.success, p.Label)