Bump to linter 0.1.51.


* `unrelated_type_equality_checks` now allows comparison between `Int64` or `Int32` and `int`
* `unnecessary_parenthesis` improved to handle cascades _in_ cascades

Change-Id: I588893132e04a706e9fc93a7a16a07005465eb1f
Reviewed-on: https://dart-review.googlesource.com/55914
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
diff --git a/DEPS b/DEPS
index 2ae24a4..2eec082 100644
--- a/DEPS
+++ b/DEPS
@@ -94,7 +94,7 @@
   "intl_tag": "0.15.2",
   "jinja2_rev": "2222b31554f03e62600cd7e383376a7c187967a1",
   "json_rpc_2_tag": "2.0.6",
-  "linter_tag": "0.1.50",
+  "linter_tag": "0.1.51",
   "logging_tag": "0.11.3+1",
   "markdown_tag": "1.1.1",
   "matcher_tag": "0.12.1+4",