Update import path of fsnotify

Rename "gopkg.in/fsnotify.v1" to "github.com/fsnotify/fsnotify"
per upstream recommendation.

See https://github.com/fsnotify/fsnotify/issues/108 for rationale.

viper.go

diff --git a/viper.go b/viper.go
index 70f8d03..df18448 100644
--- a/viper.go
+++ b/viper.go
@@ -31,12 +31,12 @@
 	"strings"
 	"time"
 
+	"github.com/fsnotify/fsnotify"
 	"github.com/kr/pretty"
 	"github.com/mitchellh/mapstructure"
 	"github.com/spf13/cast"
 	jww "github.com/spf13/jwalterweatherman"
 	"github.com/spf13/pflag"
-	"gopkg.in/fsnotify.v1"
 )
 
 var v *Viper