docs: Fix broken link in upgrade.md (cosmos#9830)

this PR (https://github.com/cosmos/cosmos-sdk/pull/9822/files) didn't actually fix the problem. The number of `..` you need depends on whether `core` or `master` is included in the URL.

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## Description

Closes: #XXXX

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### Author Checklist

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please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

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I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

docs/core/upgrade.md

@@ -12,7 +12,7 @@ Upgrade your app modules smoothly with custom in-place store migration logic. {s
 
 The Cosmos SDK uses two methods to perform upgrades.
 
-- Exporting the entire application state to a JSON file using the `export` CLI command, making changes, and then starting a new binary with the changed JSON file as the genesis file. See [Chain Upgrade Guide to v0.42](../v0.42/migrations/chain-upgrade-guide-040.html).
+- Exporting the entire application state to a JSON file using the `export` CLI command, making changes, and then starting a new binary with the changed JSON file as the genesis file. See [Chain Upgrade Guide to v0.42](https://docs.cosmos.network/v0.42/migrations/chain-upgrade-guide-040.html).
 
 - Version v0.43 and later can perform upgrades in place to significantly decrease the upgrade time for chains with a larger state. Use the [Module Upgrade Guide](../building-modules/upgrade.md) to set up your application modules to take advantage of in-place upgrades.