Update canvas and branch name (#155)

Older versions of canvas are no longer working on CI. Let's upgrade them
and reflect the rename of the `master` branch to `main`.

.github/workflows/ci.yml

@@ -4,27 +4,31 @@ on:
   pull_request: {}
   push:
     branches:
-      - master
+      - main
 
 jobs:
   tests:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     steps:
       - uses: actions/checkout@v2
         with:
           submodules: recursive
 
+      - name: Install Firefox
+        uses: browser-actions/setup-firefox@latest
+
+      - name: Install geckodriver
+        uses: browser-actions/setup-geckodriver@latest
+
       - name: Install JavaScript dependencies
         run: npm install
 
       - name: Install Python dependencies
         run: |
           python3 -m pip install --user setuptools
           python3 -m pip install --user wheel
-          python3 -m pip install --user \
-            selenium \
-            pytest
+          python3 -m pip install --user -r requirements.txt
 
       - name: Run karel.js tests
         run: npm test
@@ -41,7 +45,7 @@ jobs:
         run: (cd cpp && make test)
 
   lint:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     env:
       HOOK_TOOLS_VERSION: 20200816

.github/workflows/release.yml

@@ -8,7 +8,7 @@ on:
 jobs:
 
   release:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     steps:
       - uses: actions/checkout@v2

.nvmrc

@@ -0,0 +1 @@
+v16.17.0

cpp/json.h

@@ -1,6 +1,7 @@
 #include <iosfwd>
 #include <memory>
 #include <optional>
+#include <string>
 #include <string_view>
 #include <utility>
 #include <vector>