Update Android compileSdkVersion and buildToolsVersion

[anandprabhu]

The current Android compileSdkVersion, targetSdkVersion and buildToolsVersion uses the older but default version provided by the react-native init tool. However updating to the latest version might support possible Android build issues in scenarios where other third-party libraries require the root project to have their compiledSdkVersion and buildToolsVersion to be 25 or above. Have tested these changes in our own project and seems to be working fine without any issues.

[anandprabhu]

The below issue mentions the need to update the SDK version to 26 in detail.

facebook/react-native#17287

[HazAT]

First of all, thank you for your PR.
We already had several PRs bumping the build tools version, while I would love to merge it and already did once, we will bump it as soon as facebook raises their minimum requirement.
Until then people would need to bump it on their own.

[HazAT]

As soon this facebook/react-native#17741 is merged we can merge this PR.

[GertjanReynaert]

Can this PR be merged please? I'm currently getting this error when trying to build our app for android:

      > The SDK Build Tools revision (23.0.1) is too low for project ':react-native-sentry'. Minimum required is 25.0.0

This is on the newly released react-native 56, which upgrades a few android dependencies, so I suspect this pr will fix that issue.

cc @HazAT

[CptFabulouso]

since RN 0.56.0 this is default gradle configuration

    buildToolsVersion = "26.0.3"
    minSdkVersion = 16
    compileSdkVersion = 26
    targetSdkVersion = 26
    supportLibVersion = "26.1.0"

can we update this appropriately and merge?
oh, didn't notice previous comment..

[se-bastiaan]

Please note that the build tools in this pull request are set to 26.0.2. The latest version is 26.0.3.

[HazAT]

Thank you again for the PR, I am closing this one in favor of #452