py-urllib3: update to 1.25.1

[amake]

Update py-urllib3 to 1.25.1

This fixes a crash when py-brotli is installed:
urllib3/urllib3#1572

Tested on

macOS 10.14.4 18E226
Xcode 10.2.1 10E1001

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL?

• checked your Portfile with port lint?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?

[macportsbot]

Notifying maintainers:
@stromnov for port py-urllib3.

[macportsbot]

Travis Build #6132 Passed.

Lint results

--->  Verifying Portfile for py-urllib3
--->  0 errors and 0 warnings found.

Port py27-urllib3 success on xcode10.2. Log
Port py-urllib3 success on xcode10.2. Log
Port py34-urllib3 success on xcode10.2. Log
Port py35-urllib3 success on xcode10.2. Log
Port py36-urllib3 success on xcode10.2. Log
Port py37-urllib3 success on xcode10.2. Log
Port py27-urllib3 success on xcode9.4. Log
Port py-urllib3 success on xcode9.4. Log
Port py34-urllib3 success on xcode9.4. Log
Port py35-urllib3 success on xcode9.4. Log
Port py36-urllib3 success on xcode9.4. Log
Port py37-urllib3 success on xcode9.4. Log
Port py27-urllib3 success on xcode8.3. Log
Port py-urllib3 success on xcode8.3. Log
Port py34-urllib3 success on xcode8.3. Log
Port py35-urllib3 success on xcode8.3. Log
Port py36-urllib3 success on xcode8.3. Log
Port py37-urllib3 success on xcode8.3. Log
Port py27-urllib3 success on xcode7.3. Log
Port py-urllib3 success on xcode7.3. Log
Port py34-urllib3 success on xcode7.3. Log
Port py35-urllib3 success on xcode7.3. Log
Port py36-urllib3 success on xcode7.3. Log