Bump actions/checkout from v1 to v2 (#2075)

* Update release.yml

* Update main.yml

.github/workflows/main.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - name: Set up Python 3.7
         uses: actions/setup-python@v1
         with:
@@ -25,7 +25,7 @@ jobs:
         python-version: [2.7, 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:
@@ -61,7 +61,7 @@ jobs:
         python-version: [2.7, 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:
@@ -97,7 +97,7 @@ jobs:
         python-version: [2.7, 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:

.github/workflows/release.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Get tag
       id: tag
       run: |
@@ -34,7 +34,7 @@ jobs:
     runs-on: macos-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Get tag
       id: tag
       run: |
@@ -84,7 +84,7 @@ jobs:
     runs-on: windows-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Get tag
       id: tag
       shell: bash
@@ -143,7 +143,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@master
+        uses: actions/checkout@v2
       - name: Get tag
         id: tag
         run: |