Allow pass helper to be built for macOS

Pass is described as "The Standard Unix Password Manager", and so it can
easily run on more than just Linux. Namely, it's supported on macOS. The
CLI is identical to the Linux build, which means the Linux helper code
for Pass is fully applicable toward the macOS build - a couple of
renames being the only needed thing, purely for semantic correctness.

Jenkinsfile

@@ -47,6 +47,7 @@ pipeline {
                             sh 'make deps fmt lint test'
                             sh 'make osxcodesign'
                             sh 'make osxrelease'
+                            sh 'make pass'
                             archiveArtifacts 'release/docker-credential-*'
                         }
                     }

Makefile

@@ -27,7 +27,7 @@ secretservice:
 
 pass:
 	mkdir -p bin
-	go build -o bin/docker-credential-pass pass/cmd/main_linux.go
+	go build -o bin/docker-credential-pass pass/cmd/main.go
 
 wincred:
 	mkdir -p bin
@@ -41,6 +41,7 @@ linuxrelease:
 osxrelease:
 	mkdir -p release
 	cd bin && tar cvfz ../release/docker-credential-osxkeychain-v$(VERSION)-amd64.tar.gz docker-credential-osxkeychain
+	cd bin && tar cvfz ../release/docker-credential-pass-v$(VERSION)-osx-amd64.tar.gz docker-credential-pass
 
 winrelease:
 	mkdir -p release

pass/pass_linux.go → pass/pass.go

@@ -21,7 +21,7 @@ import (
 
 const PASS_FOLDER = "docker-credential-helpers"
 
-// Pass handles secrets using Linux secret-service as a store.
+// Pass handles secrets using secret-service as a store.
 type Pass struct{}
 
 // Ideally these would be stored as members of Pass, but since all of Pass's