README: drop Go 1.4 compatability for gocryptfs v1.3

Also drop Go 1.4 from Travis CI and update other Go
versions to latest point release.

.travis.yml

@@ -6,10 +6,9 @@ git:
 # Build with the lastest versions of Go 1.4, 1.5, 1.6, 1.7
 # See https://golang.org/dl/
 go:
-  - 1.4.3
   - 1.5.4
-  - 1.6.3
-  - 1.7.1
+  - 1.6.4
+  - 1.7.5
   - 1.8
 
 install:

README.md

@@ -138,6 +138,10 @@ RM:    4.42
 Changelog
 ---------
 
+v1.3 (not released yet)
+* Drop Go 1.4 compatability. You now need Go 1.5 (released 2015-08-19)
+  or higher to build gocryptfs.
+
 v1.2.1, 2017-02-26
 * Add an integrated speed test, `gocryptfs -speed`
 * Limit password size to 1000 bytes and reject trailing garbage after the newline