<!--- Verify first that your improvement is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Explain the problem briefly below, add suggestions to wording or structure -->
The [PSRP documentation](https://docs.ansible.com/ansible/latest/plugins/connection/psrp.html) mentions `ansible_psrp_connection_backoff` but this seems to be incorrect. The code appears to refer to `ansible_psrp_reconnection_backoff` instead (`reconnection` vs `connection`).
<!--- HINT: Did you know the documentation has an "Edit on GitHub" link on every page ? -->

##### ISSUE TYPE
- Documentation Report

##### COMPONENT NAME
<!--- Write the short name of the rst file, module, plugin, task or feature below, use your best guess if unsure -->
PSRP
lib/ansible/plugins/connection/psrp.py

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.8.0.dev0
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/root/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/lib/python2.7/dist-packages/ansible-2.8.0.dev0-py2.7.egg/ansible
  executable location = /usr/local/bin/ansible
  python version = 2.7.15rc1 (default, Nov 12 2018, 14:31:15) [GCC 7.3.0]
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below
None
```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. OS version, browser, etc. -->
Linux, Ubuntu 18.04.2 LTS

##### ADDITIONAL INFORMATION
<!--- Describe how this improves the documentation, e.g. before/after situation or screenshots -->
None.
<!--- HINT: You can paste gist.github.com links for larger files -->
if not HAS_PYPSRP:
            raise AnsibleError("pypsrp or dependencies are not installed: %s"
                               % to_native(PYPSRP_IMP_ERR))
        super(Connection, self)._connect()
        self._build_kwargs()
        display.vvv("ESTABLISH PSRP CONNECTION FOR USER: %s ON PORT %s TO %s" %
                    (self._psrp_user, self._psrp_port, self._psrp_host),
                    host=self._psrp_host)
        if not self.runspace:
            connection = WSMan(**self._psrp_conn_kwargs)
            
            host_ui = PSHostUserInterface()
            self.host = PSHost(None, None, False, "Ansible PSRP Host", None,
                               host_ui, None)
            self.runspace = RunspacePool(
                connection, host=self.host,
                configuration_name=self._psrp_configuration_name
            )
            display.vvvvv(
                "PSRP OPEN RUNSPACE: auth=%s configuration=%s endpoint=%s" %
                (self._psrp_auth, self._psrp_configuration_name,
                 connection.transport.endpoint), host=self._psrp_host
            )
            try:
                self.runspace.open()
            except AuthenticationError as e:
                raise AnsibleConnectionFailure("failed to authenticate with "
                                               "the server: %s" % to_native(e))
            except WinRMError as e:
                raise AnsibleConnectionFailure(