Bumps urllib3 from 1.23 to 1.24.2.

Sourced from urllib3's changelog.

1.24.2 (2019-04-17)

• Don't load system certificates by default when any other ca_certs, ca_certs_dir or
  ssl_context parameters are specified.

• Remove Authorization header regardless of case when redirecting to cross-site. (Issue #1510)

• Add support for IPv6 addresses in subjectAltName section of certificates. (Issue #1269)

1.24.1 (2018-11-02)

• Remove quadratic behavior within GzipDecoder.decompress() (Issue #1467)

• Restored functionality of ciphers parameter for create_urllib3_context(). (Issue #1462)

1.24 (2018-10-16)

• Allow key_server_hostname to be specified when initializing a PoolManager to allow custom SNI to be overridden. (Pull #1449)

• Test against Python 3.7 on AppVeyor. (Pull #1453)

• Early-out ipv6 checks when running on App Engine. (Pull #1450)

• Change ambiguous description of backoff_factor (Pull #1436)

• Add ability to handle multiple Content-Encodings (Issue #1441 and Pull #1442)

• Skip DNS names that can't be idna-decoded when using pyOpenSSL (Issue #1405).

• Add a server_hostname parameter to HTTPSConnection which allows for
  overriding the SNI hostname sent in the handshake. (Pull #1397)

• Drop support for EOL Python 2.6 (Pull #1429 and Pull #1430)

• Fixed bug where responses with header Content-Type: message/* erroneously
  raised HeaderParsingError, resulting in a warning being logged. (Pull #1439)

• Move urllib3 to src/urllib3 (Pull #1409)

• 1efadf4 Release 1.24.2 (#1564)
• a6ec68a Merging new release version: 1.24.1
• 0cedb3b Restore context.set_ciphers() to create_urllib3_context() (#1463)
• 0aeba3b Use bytearray to accumulate bytes from gzip (#1468)
• f8d1c78 Uninstall oclint to ensure gcc can be brew upgraded (#1464)
• cd7cfa6 Resolve pytest pluggy version conflict (#1457)
• b548abc Update changelog for 1.24 release
• ef0c745 Merging new release version: 1.24
• a0964d9 Add missing key_server_hostname variable (#1449)
• 34d8298 Test against Python 3.7 on AppVeyor (#1453)
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