Do nothing when nomodifiable (#43)

plugin/easy_align.vim

@@ -75,6 +75,12 @@ function! s:set_repeat()
 endfunction
 
 function! s:generic_easy_align_op(type, vmode, live)
+  if !&modifiable
+    if a:vmode
+      normal! gv
+    endif
+    return
+  endif
   let sel_save = &selection
   let &selection = "inclusive"