Update vendor for next release (#1343)

vendor/go.uber.org/zap/field.go

@@ -364,11 +364,17 @@ func Timep(key string, val *time.Time) Field {
 // expensive (relatively speaking); this function both makes an allocation and
 // takes about two microseconds.
 func Stack(key string) Field {
+	return StackSkip(key, 1) // skip Stack
+}
+
+// StackSkip constructs a field similarly to Stack, but also skips the given
+// number of frames from the top of the stacktrace.
+func StackSkip(key string, skip int) Field {
 	// Returning the stacktrace as a string costs an allocation, but saves us
 	// from expanding the zapcore.Field union struct to include a byte slice. Since
 	// taking a stacktrace is already so expensive (~10us), the extra allocation
 	// is okay.
-	return String(key, takeStacktrace())
+	return String(key, takeStacktrace(skip+1)) // skip StackSkip
 }
 
 // Duration constructs a field with the given key and value. The encoder