housekeeping: Update Splat v7.*

[RLittlesII]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Upgrades Splat to v7.*

What is the current behavior? (You can also link to an open issue here)

Splat is on v6.*

What is the new behavior (if this is a feature change)?

Splat is on v7.*

Does this PR introduce a breaking change?

No. It does change platform registrations for Akavache against Splat.

Please check if the PR fulfills these requirements

• The commit follows our guidelines: https://github.com/Akavache/Akavache/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Other information:

[codecov]

Codecov Report

Merging #472 into master will not change coverage.
The diff coverage is 33.33%.

@@           Coverage Diff           @@
##           master     #472   +/-   ##
=======================================
  Coverage   55.86%   55.86%           
=======================================
  Files          56       56           
  Lines        3353     3353           
  Branches      499      499           
=======================================
  Hits         1873     1873           
  Misses       1345     1345           
  Partials      135      135

Impacted Files	Coverage Δ
src/Akavache/Registrations.cs	50% <ø> (ø)	⬆️
src/Akavache.Sqlite3/Registrations.cs	80% <ø> (ø)	⬆️
...rc/Akavache.Core/Platforms/shared/Registrations.cs	100% <ø> (ø)	⬆️
....Sqlite3/SqlLiteCache/SqlRawPersistentBlobCache.cs	80% <0%> (ø)	⬆️
...kavache.Sqlite3/Operations/SqliteOperationMixin.cs	28.57% <0%> (ø)	⬆️
src/Akavache.Core/BlobCache/InMemoryBlobCache.cs	57.22% <0%> (ø)	⬆️
src/Akavache.Core/Platforms/shared/Utility.cs	23.86% <0%> (ø)	⬆️
src/Akavache.Core/DependencyResolverMixin.cs	90.9% <100%> (ø)	⬆️
src/Akavache.Core/BlobCache/BlobCache.cs	26.98% <100%> (ø)	⬆️
...avache.Core/KeyedOperations/KeyedOperationQueue.cs	52.85% <50%> (ø)	⬆️

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[RLittlesII]

@glennawatson This test passes for me locally in visual studio, and running the build script. Am I missing something obvious?