Fix IsVendor() regex generation

The regex generation introduced by
20726a1de3
had a subtle but important bug in it. In particular the ^ and ^|/
prefixes were only applied to the first regex in the OR'd groupings and
not every regex in the grouping.

We fix this by wrapping each of those OR'd groups in a new non capturing
group to ensure the prefix applies to every entry in the OR'd listing.

Additionally we add three new quick tests of IsVendor to guard against
this regression in the future.

This fixes https://github.com/go-enry/go-enry/issues/135

utils.go

@@ -213,23 +213,23 @@ func init() {
 	sb := &strings.Builder{}
 
 	// Start with group 1 - those that started with `^`
-	sb.WriteString("(?:^(?:")
+	sb.WriteString("(?:^(?:(?:")
 	sb.WriteString(caretStrings[0])
 	for _, matcher := range caretStrings[1:] {
 		sb.WriteString(")|(?:")
 		sb.WriteString(matcher)
 	}
-	sb.WriteString("))")
+	sb.WriteString(")))")
 	sb.WriteString("|")
 
 	// Now add group 2 - those that started with `(^|/)`
-	sb.WriteString("(?:(?:^|/)(?:")
+	sb.WriteString("(?:(?:^|/)(?:(?:")
 	sb.WriteString(caretSegmentStrings[0])
 	for _, matcher := range caretSegmentStrings[1:] {
 		sb.WriteString(")|(?:")
 		sb.WriteString(matcher)
 	}
-	sb.WriteString("))")
+	sb.WriteString(")))")
 	sb.WriteString("|")
 
 	// Finally add the rest

utils_test.go

@@ -17,6 +17,7 @@ func TestIsVendor(t *testing.T) {
 		expected bool
 	}{
 		{"cache/", true},
+		{"something_cache/", false},
 		{"random/cache/", true},
 		{"cache", false},
 		{"dependencies/", true},
@@ -27,6 +28,7 @@ func TestIsVendor(t *testing.T) {
 		{"random/dist/", true},
 		{"random/dist", false},
 		{"deps/", true},
+		{"foodeps/", false},
 		{"configure", true},
 		{"a/configure", true},
 		{"config.guess", true},
@@ -43,6 +45,7 @@ func TestIsVendor(t *testing.T) {
 		{"foo/bar/MochiKit.js", true},
 		{"foo/bar/dojo.js", true},
 		{"foo/env/whatever", true},
+		{"some/python/venv/", false},
 		{"foo/.imageset/bar", true},
 		{"Vagrantfile", true},
 	}