Remove the --sequential from docs

We now use the batch install method from pip directly, so it's
meaningless.

Author: oz123

docs/advanced.rst

@@ -12,7 +12,7 @@ This document covers some of Pipenv's more glorious and advanced features.
 
 - Dependencies of wheels provided in a ``Pipfile`` will not be captured by ``$ pipenv lock``.
 - There are some known issues with using private indexes, related to hashing. We're actively working to solve this problem. You may have great luck with this, however.
-- Installation is intended to be as deterministic as possible — use the ``--sequential`` flag to increase this, if experiencing issues.
+- Installation is intended to be as deterministic as possible.
 
 ☤ Specifying Package Indexes
 ----------------------------