Fix expanding LOAD_PATH in gemspec

[2maz]

Otherwise Grape::VERSION might refer to another, e.g.,
system wide installed gem version

[grape-bot]

	1 Message
📖	We really appreciate pull requests that demonstrate issues, even without a fix. That said, the next step is to try and fix the failing tests!

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[dblock]

Interesting. Care to look at the build failure? Probably unrelated, but lets exclude rails edge in that case.

[2maz]

Bundler could not find compatible versions for gem `"activerecord":
  In rails_edge.gemfile:
    arel was resolved to 10.0.0.pre, which depends on
      activerecord (>= 6.a)

To me, it does not seem to be related.
Issue lies probably in the dependency definition given in "the repository: 'rails/arel'".
Should I update the travis configuration with this PR?

[dblock]

It was fixed in #1759, rebase please.

[2maz]

updated