modules: update prometheus and tidy (#294)

also bump minimum go version and limit platform matrix in actions

.github/workflows/linter.yml

@@ -1,4 +1,10 @@
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - '**'
 name: linter
 
 jobs:

.github/workflows/tests.yml

@@ -1,4 +1,10 @@
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - '**'
 name: tests
 env:
   GO111MODULE: on
@@ -11,14 +17,19 @@ jobs:
           # support the two most recent major go versions
           - 1.x
           - 1.15.x
-        platform: [ubuntu-latest, windows-latest]
+        platform: [ubuntu-latest]
         include:
           # minimum go version that works. This is not necessarily supported in
           # any way, and will be bumped up without notice as needed.  But it at
           # least lets us know what go version should work.
-          - go-version: 1.11
+          - go-version: 1.12
             platform: ubuntu-latest
 
+          # include windows, but only with the latest Go version, since there
+          # is very little in the library that is platform specific
+          - go-version: 1.x
+            platform: windows-latest
+
           # only update test coverage stats with most recent go version on linux
           - go-version: 1.x
             platform: ubuntu-latest
@@ -28,10 +39,9 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
-      - uses: actions/setup-go@v1
+      - uses: actions/setup-go@v2
         with:
           go-version: ${{ matrix.go-version }}
-      - run: go version
 
       - name: Cache go modules
         uses: actions/cache@v2