Trim 'beta' out of go version strings

This is currently broken, so go1.6beta2 will produce `go1.6beta1`
instead of `go1.6`.

Fixes #402

Changelog.md

@@ -1,3 +1,7 @@
+# v51 2016/01/21
+
+* Trim 'beta' out of go version strings when determining major version.
+
 # v50 2016/01/19
 
 * More verbose output on save -v.

dep.go

@@ -77,6 +77,9 @@ func trimGoVersion(version string) (string, error) {
 	if len(p) < 2 {
 		return "", fmt.Errorf("Error determing major go version from: %q", version)
 	}
+	if strings.Contains(p[1], "beta") {
+		p[1] = strings.Split(p[1], "beta")[0]
+	}
 	return p[0] + "." + p[1], nil
 }
 

dep_test.go

@@ -0,0 +1,26 @@
+package main
+
+import "testing"
+
+func TestTrimGoVersion(t *testing.T) {
+	var cases = []struct {
+		in, out string
+		err     bool
+	}{
+		{in: "go1.5", out: "go1.5", err: false},
+		{in: "go1.5beta1", out: "go1.5", err: false},
+		{in: "go1.5.1", out: "go1.5", err: false},
+		{in: "devel", out: "devel", err: false},
+		{in: "boom", out: "", err: true},
+	}
+
+	for _, c := range cases {
+		mv, err := trimGoVersion(c.in)
+		if err != nil && !c.err {
+			t.Errorf("Unexpected error: %s", err)
+		}
+		if mv != c.out {
+			t.Errorf("Expected trimGoVersion(%s) == '%s', but got '%s'", c.in, c.out, mv)
+		}
+	}
+}

version.go

@@ -5,7 +5,7 @@ import (
 	"runtime"
 )
 
-const version = 50
+const version = 51
 
 var cmdVersion = &Command{
 	Name:  "version",