ci: drop go1.16

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
       matrix:
         # Do not move this line; it is referred to by README.md.
         # Versions of Go that are explicitly supported by Gonum.
-        go-version: [1.17.x, 1.16.x]
+        go-version: [1.17.x]
         platform: [ubuntu-latest, macos-latest]
         force-goarch: ["", "386"]
         tags: 

.github/workflows/codecov.yml

@@ -13,7 +13,7 @@ jobs:
     if: github.event.pull_request.merged == true
     strategy:
       matrix:
-        go-version: [1.17.x, 1.16.x]
+        go-version: [1.17.x]
         platform: [ubuntu-latest]
         tags: 
           - ""

appveyor.yml

@@ -2,7 +2,7 @@ build: off
 
 image: Visual Studio 2019
 
-stack: go 1.16
+stack: go 1.17
 
 clone_folder: c:\gopath\src\gonum.org\v1\gonum