Restrict "do" blocks a bit

This solves the problem of a "do" being detected where it's part of a
method call or a symbol.

See: vim-ruby#92

Author: AndrewRadev

etc/examples/indent/blocks.rb

@@ -1,3 +1,15 @@
+do
+  something
+end
+
+def foo
+  a_hash = {:do => 'bar'}
+end
+
+def foo(job)
+  job.do!
+end
+
 proc do |(a, b)|
   puts a
   puts b

indent/ruby.vim

@@ -66,7 +66,7 @@ let s:ruby_deindent_keywords =
 let s:end_start_regex =
       \ '\C\%(^\s*\|[=,*/%+\-|;{]\|<<\|>>\|:\s\)\s*\zs' .
       \ '\<\%(module\|class\|def\|if\|for\|while\|until\|case\|unless\|begin\):\@!\>' .
-      \ '\|\<do:\@!\>'
+      \ '\|\%(^\|[^.:@$]\)\@<=\<do:\@!\>'
 
 " Regex that defines the middle-match for the 'end' keyword.
 let s:end_middle_regex = '\<\%(ensure\|else\|\%(\%(^\|;\)\s*\)\@<=\<rescue:\@!\>\|when\|elsif\):\@!\>'