Fix text field not always adjusting size for error label

The first time the error was shown on some text fields, the field didn't adjust its height to fit the error text.

Author: stephsharp

MaterialTextField/MFTextField.m

@@ -148,9 +148,7 @@ - (void)setupErrorConstraints
 {
     self.errorLabelTopConstraint = [self.errorLabel.topAnchor constraintEqualToAnchor:self.topAnchor
                                                                              constant:[self topPaddingForErrorLabelHidden:!self.hasError]];
-    NSLayoutConstraint *bottom = [self.errorLabel.bottomAnchor constraintGreaterThanOrEqualToAnchor:self.bottomAnchor];
-    bottom.priority = 900;
-
+    NSLayoutConstraint *bottom = [self.errorLabel.bottomAnchor constraintEqualToAnchor:self.bottomAnchor];
     NSLayoutConstraint *leading = [self.errorLabel.leadingAnchor constraintEqualToAnchor:self.leadingAnchor
                                                                                 constant:self.errorPadding.width];
     NSLayoutConstraint *trailing = [self.trailingAnchor constraintGreaterThanOrEqualToAnchor:self.errorLabel.trailingAnchor