Fix Former::plaintext() with Bootstrap 4 (#602)

Replace 'form-control-static' CSS class with 'form-control-plaintext'

Usage with Laravel:

{!! Former::open()->method('GET') !!}
  {!! Former::plaintext('test_static')->value('Plain Text') !!}
{!! Former::close() !!}

Reference:
https://getbootstrap.com/docs/4.5/components/forms/#readonly-plain-text

src/Former/Framework/TwitterBootstrap4.php

@@ -295,7 +295,7 @@ public function getUneditableClasses()
 	 */
 	public function getPlainTextClasses()
 	{
-		return 'form-control-static';
+		return 'form-control-plaintext';
 	}
 
 	/**

tests/Fields/PlainTextTest.php

@@ -72,6 +72,22 @@ public function matchPlainTextInput()
 		);
 	}
 
+	/**
+	 * Matches an plain text input as a p tag
+	 *
+	 * @return array
+	 */
+	public function matchPlainTextInputWithBS4()
+	{
+	return array(
+			'tag'        => 'div',
+			'content'    => 'bar',
+			'attributes' => array(
+				'class' => 'form-control-plaintext',
+			),
+		);
+	}
+
 	/**
 	 * Matches an plain text input as a div tag
 	 *
@@ -126,6 +142,21 @@ protected function formStaticGroup(
 		return $this->formGroup($input, $label);
 	}
 
+	/**
+	 * Matches a Form Static Group
+	 *
+	 * @param  string $input
+	 * @param  string $label
+	 *
+	 * @return boolean
+	 */
+	protected function formStaticGroupForBS4(
+		$input = '<div class="form-control-plaintext" id="foo">bar</div>',
+		$label = '<label for="" class="col-form-label col-lg-2 col-sm-4">Foo</label>'
+	) {
+		return $this->formGroupWithBS4($input, $label);
+	}
+
 	/**
 	 * Matches a Form Static Group with HTML value escaped
 	 *
@@ -188,6 +219,18 @@ public function testCanCreatePlainTextFieldsWithBS3()
 		$this->assertEquals($matcher, $input);
 	}
 
+	public function testCanCreatePlainTextFieldsWithBS4()
+	{
+		$this->former->framework('TwitterBootstrap4');
+		$input = $this->former->plaintext('foo')->value('bar')->__toString();
+
+		$this->assertHTML($this->matchPlainLabelWithBS3(), $input);
+		$this->assertHTML($this->matchPlainTextInputWithBS4(), $input);
+
+		$matcher = $this->formStaticGroupForBS4();
+		$this->assertEquals($matcher, $input);
+	}
+
 	public function testCanCreatePlainTextFieldsWithHtmlValueEscaped()
 	{
 		$this->former->framework('TwitterBootstrap3');

tests/TestCases/FormerTests.php

@@ -302,6 +302,21 @@ protected function formGroup(
 		return '<div class="form-group">'.$label.'<div class="col-lg-10 col-sm-8">'.$input.'</div></div>';
 	}
 
+	/**
+	 * Matches a Form Group
+	 *
+	 * @param  string $input
+	 * @param  string $label
+	 *
+	 * @return boolean
+	 */
+	protected function formGroupWithBS4(
+		$input = '<input type="text" name="foo" id="foo">',
+		$label = '<label for="foo" class="col-form-label col-lg-2 col-sm-4">Foo</label>'
+	) {
+		return '<div class="form-group row">'.$label.'<div class="col-lg-10 col-sm-8">'.$input.'</div></div>';
+	}
+
 	/**
 	 * Matches a required Control Group
 	 *