changed xref id to match the target

Author: moisedk

pretext/Files/AlternativeFileReadingMethods.ptx

@@ -45,7 +45,7 @@
 1870  -0.28  6.6E-7
 1880  -0.24
 &gt;&gt;&gt;</pre>
-  <table xml:id="files_files_filemethods2a">
+  <table xml:id="files_filemethods2a">
     <tabular>
       <row header="yes">
         <cell>