fix: define web dependency properly

[johnmartel]

This commit fixes the following error when fetching dependencies:

Invalid version constraint: Expected version number after ">=" in
">=^0.5.1 <2.0.0", got "^0.5.1 <2.0.0".

[docs-page]

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docs.page/lyokone/flutterlocation~1001

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[johnmartel]

To actually use this fix, add the following dependecy override in pubspec.yaml:

dependencies:
  location: 7.0.0

dependency_overrides:
  location_web:
    # fixes dependency problem on web: 0.5.1
    # fix has not been released yet
    git:
      url: https://github.com/valian-ca/flutterlocation.git
      ref: 457fa290c37d360a62370d958db7bf1aa653e502
      path: packages/location_web

Fixes: #983

[bartekpacia]

superseded by #1002 and #1003