Bump okhttp from 3.2.0 to 4.0.0

[dependabot-preview]

Bumps okhttp from 3.2.0 to 4.0.0.

Changelog

Sourced from okhttp's changelog.

Version 4.0.0

2019-06-26

This release upgrades OkHttp to Kotlin. We tried our best to make fast and safe to upgrade
from OkHttp 3.x. We wrote an [upgrade guide][upgrading_to_okhttp_4] to help with the migration and a
[blog post][okhttp4_blog_post] to explain it.

• Fix: Target Java 8 bytecode for Java and Kotlin.

Version 4.0.0-RC3

2019-06-24

• Fix: Retain binary-compatibility in okhttp3.internal.HttpMethod. Naughty third party SDKs
  import this and we want to ease upgrades for their users.

Version 4.0.0-RC2

2019-06-21

• New: Require Kotlin 1.3.40.
• New: Change the Kotlin API from File.toRequestBody() to File.asRequestBody() and
  BufferedSource.toResponseBody() to BufferedSource.asResponseBody(). If the returned value
  is a view of what created it, we use as.
• Fix: Permit response codes of zero for compatibility with OkHttp 3.x.
• Fix: Change the return type of MockWebServer.takeRequest() to be nullable.
• Fix: Make Call.clone() public to Kotlin callers.

Version 4.0.0-RC1

2019-06-03

• First stable preview of OkHttp 4.

Version 3.14.2

2019-05-19

• Fix: Lock in a route when recovering from an HTTP/2 connection error. We had a bug where two
  calls that failed at the same time could cause OkHttp to crash with a NoSuchElementException
  instead of the expected IOException.

• Fix: Don't crash with a NullPointerException when formatting an error message describing a
  truncated response from an HTTPS proxy.

... (truncated)

Commits

• 911c5bf Prepare for release 4.0.0.
• fafcf4b Merge pull request #5242 from yschimke/prefer_jdk11
• c88f9a9 Prefer JDK 11 for tests
• b7e6f4f Fix conscrypt tests (#5241)
• d81ec0f OkHttpClientTestRule check connectionCount instead of idle (#5226)
• d1b99e6 Merge pull request #5239 from square/jakew/eleven/2019-06-25
• 24c0575 Merge pull request #5238 from square/jakew/eight/2019-06-25
• 4607fe8 Run error-prone on JDK 11
• 0bdd679 Target Java 8 bytecode for Java and Kotlin
• 3217919 Allow nullable on Util.close (#5224)
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #70.