fix(struct_tags): edge case with structs declared as var (#99)

* fix(struct_tags): edge case with structs declared as var

* test: test it and fix it

* fixup! test: test it and fix it

* fixup! fix(struct_tags): edge case with structs declared as var

* fixup! test: test it and fix it

spec/fixtures/tags/svar_input.go

@@ -0,0 +1,11 @@
+package main
+
+func main() {
+	s := struct {
+		API string
+		Key string
+	}{
+		API: "api.com",
+		Key: "key",
+	}
+}

spec/fixtures/tags/svar_output.go

@@ -0,0 +1,11 @@
+package main
+
+func main() {
+	s := struct {
+		API string `xml:"api"`
+		Key string `xml:"key"`
+	}{
+		API: "api.com",
+		Key: "key",
+	}
+}

spec/fixtures/tags/var_input.go

@@ -0,0 +1,8 @@
+package main
+
+func main() {
+	var a struct {
+		TestField1 string
+		TestField2 string
+	}
+}

spec/fixtures/tags/var_output.go

@@ -0,0 +1,8 @@
+package main
+
+func main() {
+	var a struct {
+		TestField1 string `yaml:"test_field_1"`
+		TestField2 string `yaml:"test_field_2"`
+	}
+}