Node API docs: Use consistent English tense

[Anviking]

Description

Continuation on cardano-foundation/cardano-wallet#346, but for the node
API.

The changes in cardano-wallet might not have been backported to
cardano-sl yet.

Linked issue

cardano-foundation/cardano-wallet#333

Type of change

• 🐞 Bug fix (non-breaking change which fixes an issue)
• 🛠 New feature (non-breaking change which adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)
• 🏭 Refactoring that does not change existing functionality but does improve things like code readability, structure etc
• 🔨 New or improved tests for existing code
• ⛑ git-flow chore (backport, hotfix, etc)

Developer checklist

• I have read the style guide document, and my code follows the code style of this project.
• If my code deals with exceptions, it follows the guidelines.
• I have updated any documentation accordingly, if needed. Documentation changes can be reflected in opening a PR on cardanodocs.com, amending the inline Haddock comments, any relevant README file or one of the document listed in the docs directory.
• CHANGELOG entry has been added and is linked to the correct PR on GitHub.

Testing checklist

• I have added tests to cover my changes.
• All new and existing tests passed.

QA Steps

stack build cardano-sl-node --ghc-options=-optl-Wl,-dead_strip_dylibs
stack exec cardano-node-simple -- --topology=wallet/topology-examples/testnet.yaml \
                                                                     --configuration-key=mainnet_staging_short_epoch_full \
                                                                     --log-config=log-configs/cluster.yaml       \
                                                                     --node-api-address           127.0.0.1:8080 \
                                                                     --node-doc-address           127.0.0.1:8180 \
                                                                                                                 \
                                                                     --tlsca       scripts/tls-files/ca.crt      \
                                                                     --tlscert     scripts/tls-files/server.crt  \
                                                                     --tlskey      scripts/tls-files/server.key  \

Screenshots (if available)

How to merge

Send the message bors r+ to merge this PR. For more information, see
docs/how-to/bors.md.

[intricate]

Makes sense to me.