Prefer 'operation' to 'query'

[davetapley]

Per the docs

The operation type is either query, mutation, or subscription and describes what type of operation you're intending to do.

However many places in the README, and the library itself conflate 'query' with 'operation'. For example:

---

Under More Examples we see:

const { query } = require('graphqurl');

query(
  {
    query: `
      mutation ($id_insert_input: String!, $column_insert_input: String!) {

And later:

query(
  {
    query: 'subscription { table { column } }',

---

Under CLI we see:

gq \
     [snip]
     --variableFile='./queryVariables.json' \
     --queryFile='./query.gql

... but there is nothing to stop './query.gql containing a mutation.

---

In the code itself there is a red flag here:

graphqurl/src/query.js

Line 75 in dbe963c

if (queryType === 'query') {

graphqurl/src/query.js

Line 83 in dbe963c

} else if (queryType === 'mutation') {

graphqurl/src/query.js

Line 91 in dbe963c

} else if (queryType === 'subscription') {

⬆️ per the doc linked at the start of this issue I propose this should definitely be operationType.

---

Would you accept a PR to:

1. Change the README to prefer 'operation' to 'query'.

2. Rename query.js to operation.js, and:
   Re-export operation as query (to prevent API breaking change) in

   graphqurl/src/index.js

   Lines 4 to 5 in dbe963c

   	module.exports = {
   	query,

3. Add --operationFile to the CLI as an alias of --queryFile

❓