Update file node examples according to node name change

[HiroyasuNishiyama]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

In recent Node-RED release, name of file and file-in node changed to read file and write file. But examples of these nodes uses old name. This PR fixes these node names.
This PR also fixes minor typo in examples.

Proposed changes

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage remained the same at 67.361% when pulling 9ac4e5c on node-red-hitachi:fix-file-node-example into b14c42b on node-red:master.