Make pylintrc compatible with version in op-desafios.

- Added unspecified-encoding and consider-using-with exclusions.
- The presubmit checks in op-desafios use the latest pylint version,
  which deprecated a number of options. This test uses a fixed version
  (from docker), so we can't use the same file in both repos anymore.
  This is a temporary condition until we update pylint here to match the
  version in op-desafios.

config/pylint3.rc

@@ -60,6 +60,7 @@ disable=apply-builtin,
         bad-python3-import,
         basestring-builtin,
         buffer-builtin,
+        consider-using-with,
         cmp-builtin,
         cmp-method,
         coerce-builtin,
@@ -134,6 +135,7 @@ disable=apply-builtin,
         unichr-builtin,
         unicode-builtin,
         unpacking-in-except,
+        unspecified-encoding,
         useless-suppression,
         using-cmp-argument,
         xrange-builtin,