Update references to master branch

.github/pull_request_template.md

@@ -7,7 +7,7 @@ below :-).
 ### Documentation PR
 
 - [ ] I've [seen the `doc/README.md` file](https://github.com/plotly/plotly.py/blob/master/doc/README.md)
-- [ ] This change runs in the current version of Plotly on PyPI and targets the `doc-prod` branch OR it targets the `master` branch
+- [ ] This change runs in the current version of Plotly on PyPI and targets the `doc-prod` branch OR it targets the `main` branch
 - [ ] If this PR modifies the first example in a page or adds a new one, it is a `px` example if at all possible
 - [ ] Every new/modified example has a descriptive title and motivating sentence or paragraph
 - [ ] Every new/modified example is independently runnable

CONTRIBUTING.md

@@ -198,7 +198,7 @@ a PR as follows.
 
 ### Making a Development Branch
 
-Third, *don't* work in the `master` branch. As soon as you get your master branch ready, run:
+Third, *don't* work in the `main` branch. As soon as you get your main branch ready, run:
 
 **DO THIS (but change the branch name)**
 ```bash

RELEASE.md

@@ -33,7 +33,7 @@ Manually update the versions to `X.Y.Z` in the files specified below.
  - Create a tag for Github release
    + `git tag vX.Y.Z`
    + `git push --atomic origin release-X.Y.Z vX.Y.Z`
- - Create a Github pull request from `release-X.Y.Z` to `master` and wait for CI to be green
+ - Create a Github pull request from `release-X.Y.Z` to `main` and wait for CI to be green
 
 ### Download and QA CI Artifacts
 
@@ -62,7 +62,7 @@ Publishing to PyPI:
 
 ### Merge the PR and make a Release
 
-1. Merge the pull request you created above into `master`
+1. Merge the pull request you created above into `main`
 2. Go to https://github.com/plotly/plotly.py/releases and "Draft a new release"
 3. Enter the `vX.Y.Z` tag you created already above and make "Release title" the same string as the tag.
 4. Copy the changelog section for this version as the "Describe this release"
@@ -73,8 +73,8 @@ Publishing to PyPI:
     - `doc/python/getting-started.md`
     - `doc/apidoc/conf.py`
     - `doc/requirements.txt`
-2. `doc-prod` should already have been merged on a regular basis into `master`, but
-start by doing it first if not. Then merge `master` into `doc-prod` to deploy the doc related
+2. `doc-prod` should already have been merged on a regular basis into `main`, but
+start by doing it first if not. Then merge `main` into `doc-prod` to deploy the doc related
 to features in the release.
 3. in a clone of the [`graphing-library-docs` repo](https://github.com/plotly/graphing-library-docs):
     1. bump the version of Plotly.py in  `_data/pyversion.json`

doc/README.md

@@ -41,7 +41,7 @@ released, or which has just been included but not yet released.
   your branch off the `doc-prod` branch and open your pull request against this
   `doc-prod` branch.
 - Case of a new (not released yet) feature: start your branch / pull request
-  against the `master` branch. `master` and `doc-prod` will be synchronized at
+  against the `main` branch. `main` and `doc-prod` will be synchronized at
   release time, so that the documentation of the feature is only deployed when
   it is available in a released version of `plotly.py`.