Documentation fixes

- Object.freeze creates a readonly object that doesn't play will in TS
3.2
- Gitignore docs directory

Author: cblanc

.gitignore

@@ -1,3 +1,4 @@
+#
 # Logs
 logs
 *.log
@@ -59,4 +60,5 @@ dist
 .cache
 
 .DS_Store
+docs
 

lib/index.ts

@@ -62,7 +62,7 @@ type InvalidPostcode = {
   unit: null;
 };
 
-const invalidPostcode: InvalidPostcode = Object.freeze({
+const invalidPostcode: InvalidPostcode = {
   valid: false,
   postcode: null,
   incode: null,
@@ -72,7 +72,7 @@ const invalidPostcode: InvalidPostcode = Object.freeze({
   subDistrict: null,
   sector: null,
   unit: null
-});
+};
 
 /**
  * Return first elem of input is RegExpMatchArray or null if input null