vendor: update all dependencies

* Update all dependencies
  * Remove all `[[constraint]]` from Gopkg.toml
  * Add in the minimum number of `[[override]]` to build
  * Remove go get of github.com/inconshreveable/mousetrap as it is vendored
  * Update docs with new policy on constraints

vendor/golang.org/x/sys/unix/syscall.go

@@ -24,14 +24,14 @@
 // holds a value of type syscall.Errno.
 package unix // import "golang.org/x/sys/unix"
 
+import "strings"
+
 // ByteSliceFromString returns a NUL-terminated slice of bytes
 // containing the text of s. If s contains a NUL byte at any
 // location, it returns (nil, EINVAL).
 func ByteSliceFromString(s string) ([]byte, error) {
-	for i := 0; i < len(s); i++ {
-		if s[i] == 0 {
-			return nil, EINVAL
-		}
+	if strings.IndexByte(s, 0) != -1 {
+		return nil, EINVAL
 	}
 	a := make([]byte, len(s)+1)
 	copy(a, s)