Update dependencies, enable pruning for vendor/

So, `dep` got an nice new feature to remove tests and non-go files from
`vendor/`, and this brings the size of the vendor directory from ~300MiB
down to ~20MiB. We don that now.

vendor/github.com/dustin/go-humanize/ftoa.go

@@ -1,6 +1,9 @@
 package humanize
 
-import "strconv"
+import (
+	"strconv"
+	"strings"
+)
 
 func stripTrailingZeros(s string) string {
 	offset := len(s) - 1
@@ -17,7 +20,27 @@ func stripTrailingZeros(s string) string {
 	return s[:offset+1]
 }
 
+func stripTrailingDigits(s string, digits int) string {
+	if i := strings.Index(s, "."); i >= 0 {
+		if digits <= 0 {
+			return s[:i]
+		}
+		i++
+		if i+digits >= len(s) {
+			return s
+		}
+		return s[:i+digits]
+	}
+	return s
+}
+
 // Ftoa converts a float to a string with no trailing zeros.
 func Ftoa(num float64) string {
 	return stripTrailingZeros(strconv.FormatFloat(num, 'f', 6, 64))
 }
+
+// FtoaWithDigits converts a float to a string but limits the resulting string
+// to the given number of decimal places, and no trailing zeros.
+func FtoaWithDigits(num float64, digits int) string {
+	return stripTrailingZeros(stripTrailingDigits(strconv.FormatFloat(num, 'f', 6, 64), digits))
+}