Update GitHub action checkout to v2 for better performance

Author: jasongrout

.github/workflows/lint.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Use Node.js 10.x
       uses: actions/setup-node@v1
       with:

.github/workflows/tests.yml

@@ -7,7 +7,7 @@ jobs:
     name: Documentation
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Set up Python
       uses: actions/setup-python@v1
       with:
@@ -33,7 +33,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Use Node.js 10.x
       uses: actions/setup-node@v1
       with:
@@ -87,7 +87,7 @@ jobs:
         python-version: [3.5, 3.6, 3.7, 3.8]
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v1
       with:
@@ -110,7 +110,7 @@ jobs:
     name: Message Specification
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Set up Python
       uses: actions/setup-python@v1
       with: