gatsby-plugin-typography no longer works with default config

[Sekhmet]

Description

After this PR #10545 gatsby-plugin-typography no longer works with default config.

Steps to reproduce

1. Follow this tutorial: https://www.gatsbyjs.org/tutorial/part-two/
2. Stop after modifying gatsby-config.js for the first time (version without explicit pathToConfigModule).
3. Visit http://localhost:8000/

Expected result

Page should load, typography CSS should be injected.

Actual result

Error is thrown:

Unhandled Rejection (TypeError): Cannot read property 'injectStyles' of undefined
./node_modules/gatsby-plugin-typography/gatsby-browser.js.exports.onClientEntry
node_modules/gatsby-plugin-typography/gatsby-browser.js:21
(anonymous function)
/home/sekhmet/Workspace/tutorial-part-two/.cache/api-runner-browser.js:52

Environment

  System:
    OS: Linux 4.18 Pop!_OS 18.10
    CPU: (16) x64 AMD Ryzen 7 2700X Eight-Core Processor
    Shell: 5.5.1 - /usr/bin/zsh
  Binaries:
    Node: 10.14.2 - ~/.nvm/versions/node/v10.14.2/bin/node
    Yarn: 1.12.3 - /usr/bin/yarn
    npm: 6.4.1 - ~/.nvm/versions/node/v10.14.2/bin/npm
  Browsers:
    Chrome: 71.0.3578.98
    Firefox: 64.0
  npmPackages:
    gatsby: ^2.0.74 => 2.0.74 
    gatsby-plugin-typography: ^2.2.3 => 2.2.3 
  npmGlobalPackages:
    gatsby-cli: 2.4.7