Add exception for version (#10)

### What
Add exception for global variables named version.

### Why
Current best practice for setting the version of a Go executable requires a global variable. This change adds a narrow exception for variables name version exactly.

README.md

@@ -13,6 +13,13 @@ Global variables are an input to functions that is not visible in the functions
 https://peter.bourgon.org/blog/2017/06/09/theory-of-modern-go.html
 https://twitter.com/davecheney/status/871939730761547776
 
+### Exceptions
+
+There are very few exceptions to the global variable rule. This tool will ignore the following patterns:
+ * Variables with an `Err` prefix
+ * Variables named `_`
+ * Variables named `version`
+
 ## Install
 
 ```

check_no_globals.go

@@ -11,7 +11,7 @@ import (
 )
 
 func isWhitelisted(i *ast.Ident) bool {
-	return i.Name == "_" || looksLikeError(i)
+	return i.Name == "_" || i.Name == "version" || looksLikeError(i)
 }
 
 // looksLikeError returns true if the AST identifier starts

check_no_globals_test.go

@@ -105,6 +105,13 @@ func TestCheckNoGlobals(t *testing.T) {
 				"testdata/8/code.go:30 declaredErr is a global variable",
 			},
 		},
+		{
+			path: "testdata/9",
+			wantMessages: []string{
+				"testdata/9/code.go:3 Version is a global variable",
+				"testdata/9/code.go:4 version22 is a global variable",
+			},
+		},
 		{
 			path:         ".",
 			wantMessages: nil,
@@ -135,6 +142,8 @@ func TestCheckNoGlobals(t *testing.T) {
 				"testdata/8/code.go:20 myVarError is a global variable",
 				"testdata/8/code.go:21 customErr is a global variable",
 				"testdata/8/code.go:30 declaredErr is a global variable",
+				"testdata/9/code.go:3 Version is a global variable",
+				"testdata/9/code.go:4 version22 is a global variable",
 			},
 		},
 	}

testdata/9/code.go

@@ -0,0 +1,5 @@
+package code
+
+var Version string
+var version22 string
+var version string