Fix square bracket handling in string_array

Same issue fixed in 13e924de for string_slice.

string_array.go

diff --git a/string_array.go b/string_array.go
index f320f2e..93b4e43 100644
--- a/string_array.go
+++ b/string_array.go
@@ -2,7 +2,6 @@
 
 import (
 	"fmt"
-	"strings"
 )
 
 var _ = fmt.Fprint
@@ -40,7 +39,7 @@
 }
 
 func stringArrayConv(sval string) (interface{}, error) {
-	sval = strings.Trim(sval, "[]")
+	sval = sval[1 : len(sval)-1]
 	// An empty string would cause a array with one (empty) string
 	if len(sval) == 0 {
 		return []string{}, nil

string_array_test.go

diff --git a/string_array_test.go b/string_array_test.go
index 3e3eb74..1ceac8c 100644
--- a/string_array_test.go
+++ b/string_array_test.go
@@ -192,3 +192,42 @@
 		}
 	}
 }
+
+func TestSAWithSquareBrackets(t *testing.T) {
+	var sa []string
+	f := setUpSAFlagSet(&sa)
+
+	in := []string{"][]-[", "[a-z]", "[a-z]+"}
+	expected := []string{"][]-[", "[a-z]", "[a-z]+"}
+	argfmt := "--sa=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	arg3 := fmt.Sprintf(argfmt, in[2])
+	err := f.Parse([]string{arg1, arg2, arg3})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	if len(expected) != len(sa) {
+		t.Fatalf("expected number of sa to be %d but got: %d", len(expected), len(sa))
+	}
+	for i, v := range sa {
+		if expected[i] != v {
+			t.Fatalf("expected sa[%d] to be %s but got: %s", i, expected[i], v)
+		}
+	}
+
+	values, err := f.GetStringArray("sa")
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	if len(expected) != len(values) {
+		t.Fatalf("expected number of values to be %d but got: %d", len(expected), len(values))
+	}
+	for i, v := range values {
+		if expected[i] != v {
+			t.Fatalf("expected got sa[%d] to be %s but got: %s", i, expected[i], v)
+		}
+	}
+}