whitespace: do not detect '=======' as conflict marker for rst files

closes #2014

autoload/airline/extensions/whitespace.vim

@@ -50,7 +50,12 @@ endfunction
 function! s:conflict_marker()
   " Checks for git conflict markers
   let annotation = '\%([0-9A-Za-z_.:]\+\)\?'
-  let pattern = '^\%(\%(<\{7} '.annotation. '\)\|\%(=\{7\}\)\|\%(>\{7\} '.annotation.'\)\)$'
+  if &ft is# 'rst'
+    " rst filetypes use '=======' as header
+    let pattern = '^\%(\%(<\{7} '.annotation. '\)\|\%(>\{7\} '.annotation.'\)\)$'
+  else
+    let pattern = '^\%(\%(<\{7} '.annotation. '\)\|\%(=\{7\}\)\|\%(>\{7\} '.annotation.'\)\)$'
+  endif
   return search(pattern, 'nw')
 endfunction