fix: changed vidibility to private

All constants at these scopes are private and when was executed cs:fix,
was accidentally defined as public.

Signed-off-by: Vitor Mattos <[email protected]>

Author: vitormattos

src/FdfFile.php

@@ -16,13 +16,13 @@
 class FdfFile extends File
 {
     // FDF file header
-    public const FDF_HEADER = <<<FDF
+    private const FDF_HEADER = <<<FDF
 %FDF-1.2
 1 0 obj<</FDF<< /Fields[
 FDF;
 
     // FDF file footer
-    public const FDF_FOOTER = <<<FDF
+    private const FDF_FOOTER = <<<FDF
 ] >> >>
 endobj
 trailer

src/XfdfFile.php

@@ -53,15 +53,15 @@
 class XfdfFile extends File
 {
     // XFDF file header
-    public const XFDF_HEADER = <<<FDF
+    private const XFDF_HEADER = <<<FDF
 <?xml version="1.0" encoding="UTF-8"?>
 <xfdf xmlns="http://ns.adobe.com/xfdf/" xml:space="preserve">
 <fields>
 
 FDF;
 
     // XFDF file footer
-    public const XFDF_FOOTER = <<<FDF
+    private const XFDF_FOOTER = <<<FDF
 </fields>
 </xfdf>