update all the things to go 1.15

.github/workflows/pr.yml

@@ -8,10 +8,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
 
-    - name: Set up Go 1.13
+    - name: Set up Go 1.15
       uses: actions/setup-go@v1
       with:
-        go-version: 1.13
+        go-version: 1.15
       id: go
 
     - name: Check out code into the Go module directory

.github/workflows/tests.yml

@@ -8,10 +8,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
 
-    - name: Set up Go 1.13
+    - name: Set up Go 1.15
       uses: actions/setup-go@v1
       with:
-        go-version: 1.13
+        go-version: 1.15
       id: go
 
     - name: Check out code into the Go module directory

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.13-alpine
+FROM golang:1.15-alpine
 
 RUN mkdir /user && \
     echo 'nobody:x:65534:65534:nobody:/:' > /user/passwd && \