Bump okhttp from 3.12.1 to 3.13.1 in /examples

[dependabot-preview]

Bumps okhttp from 3.12.1 to 3.13.1.

Changelog

Sourced from okhttp's changelog.

Version 3.13.1

2019-02-05

• Fix: Don't crash when using a custom X509TrustManager or SSLSocket on Android. When we
  removed obsolete code for Android 4.4 we inadvertently also removed support for custom
  subclasses. We've restored that support!

Version 3.13.0

2019-02-04

• This release bumps our minimum requirements to Java 8+ or Android 5+. Cutting off old
  devices is a serious change and we don't do it lightly! [This post][require_android_5] explains
  why we're doing this and how to upgrade.

  The OkHttp 3.12.x branch will be our long-term branch for Android 2.3+ (API level 9+) and Java
  7+. These platforms lack support for TLS 1.2 and should not be used. But because upgrading is
  difficult we will backport critical fixes to the 3.12.x branch through December 31, 2020.

• TLSv1 and TLSv1.1 are no longer enabled by default. Major web browsers are working towards
  removing these versions altogether in early 2020. If your servers aren't ready yet you can
  configure OkHttp 3.13 to allow TLSv1 and TLSv1.1 connections:

  OkHttpClient client = new OkHttpClient.Builder()
      .connectionSpecs(Arrays.asList(ConnectionSpec.COMPATIBLE_TLS))
      .build();
  

• New: You can now access HTTP trailers with Response.trailers(). This method may only be called
  after the entire HTTP response body has been read.

• New: Upgrade to Okio 1.17.3. If you're on Kotlin-friendly Okio 2.x this release requires 2.2.2
  or newer.

  implementation("com.squareup.okio:okio:1.17.3")

• Fix: Don't miss cancels when sending HTTP/2 request headers.

• Fix: Don't miss whole operation timeouts when calls redirect.

• Fix: Don't leak connections if web sockets have malformed responses or if onOpen() throws.

• Fix: Don't retry when request bodies fail due to FileNotFoundException.

• Fix: Don't crash when URLs have IPv4-mapped IPv6 addresses.

• Fix: Don't crash when building HandshakeCertificates on Android API 28.

• Fix: Permit multipart file names to contain non-ASCII characters.

• New: API to get MockWebServer's dispatcher.

• New: API to access headers as java.time.Instant.

... (truncated)

Commits

• d28d2ce [maven-release-plugin] prepare release parent-3.13.1
• c93cb5a Merge pull request #4593 from square/jwilson.0205.restore_custom_tls
• ad8d809 Restore support for custom trust managers on Android
• ffbe3ca Bump docs to 3.13.0
• 5ecd590 [maven-release-plugin] prepare for next development iteration
• d556615 [maven-release-plugin] prepare release parent-3.13.0
• b10e9c8 Merge pull request #4590 from square/jwilson.0204.drop_the_bom
• 3f890a4 Drop the okhttp-bom module
• 293700e Merge pull request #4589 from square/jwilson.0204.release_glitches
• 2b5337d Fix some maven problems that are blocking the 3.13 release
• Additional commits viewable in compare view

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