Search current directory for config file by default

As of 2015-08-16, Viper no longer searches the CWD
for config file by default to avoid unintended surprises,
but Hugo relies on the original behaviour.

Fixed by calling

    viper.AddConfigPath(".")

at the appropriate place.

See spf13/viper#73 for more information.

Fixes gohugoio#1363

commands/hugo.go

@@ -165,7 +165,12 @@ func LoadDefaultSettings() {
 // InitializeConfig initializes a config file with sensible default configuration flags.
 func InitializeConfig() {
 	viper.SetConfigFile(CfgFile)
-	viper.AddConfigPath(Source)
+	// See https://github.com/spf13/viper/issues/73#issuecomment-126970794
+	if Source == "" {
+		viper.AddConfigPath(".")
+	} else {
+		viper.AddConfigPath(Source)
+	}
 	err := viper.ReadInConfig()
 	if err != nil {
 		jww.ERROR.Println("Unable to locate Config file. Perhaps you need to create a new site. Run `hugo help new` for details")