Fix panic when setting uint from int value

mapstructure.go

diff --git a/mapstructure.go b/mapstructure.go
index 11bde03..8c05dd9 100644
--- a/mapstructure.go
+++ b/mapstructure.go
@@ -137,7 +137,7 @@
 		if valKind == reflect.Int {
 			val.SetInt(dataVal.Int())
 		} else {
-			val.SetUint(uint64(dataVal.Uint()))
+			val.SetUint(uint64(dataVal.Int()))
 		}
 	case reflect.Uint:
 		if valKind == reflect.Int {

mapstructure_test.go

diff --git a/mapstructure_test.go b/mapstructure_test.go
index 453fc56..945e5d8 100644
--- a/mapstructure_test.go
+++ b/mapstructure_test.go
@@ -5,6 +5,7 @@
 type Basic struct {
 	Vstring string
 	Vint    int
+	Vuint   uint
 	Vbool   bool
 	Vextra  string
 	vsilent bool
@@ -44,6 +45,7 @@
 	input := map[string]interface{}{
 		"vstring": "foo",
 		"vint":    42,
+		"Vuint":   42,
 		"vbool":   true,
 		"vsilent": true,
 		"vdata":   42,
@@ -64,6 +66,10 @@
 		t.Errorf("vint value should be 42: %#v", result.Vint)
 	}
 
+	if result.Vuint != 42 {
+		t.Errorf("vuint value should be 42: %#v", result.Vuint)
+	}
+
 	if result.Vbool != true {
 		t.Errorf("vbool value should be true: %#v", result.Vbool)
 	}