Fix error grammar

Fixes #56

matrix.go

@@ -137,7 +137,7 @@ func (m matrix) Augment(right matrix) (matrix, error) {
 }
 
 // errMatrixSize is returned if matrix dimensions are doesn't match.
-var errMatrixSize = errors.New("matrix sizes does not match")
+var errMatrixSize = errors.New("matrix sizes do not match")
 
 func (m matrix) SameSize(n matrix) error {
 	if len(m) != len(n) {

reedsolomon.go

@@ -391,7 +391,7 @@ var ErrShardNoData = errors.New("no shard data")
 
 // ErrShardSize is returned if shard length isn't the same for all
 // shards.
-var ErrShardSize = errors.New("shard sizes does not match")
+var ErrShardSize = errors.New("shard sizes do not match")
 
 // checkShards will check if shards are the same size
 // or 0, if allowed. An error is returned if this fails.

streaming.go

@@ -256,7 +256,7 @@ func trimShards(in [][]byte, size int) [][]byte {
 
 func readShards(dst [][]byte, in []io.Reader) error {
 	if len(in) != len(dst) {
-		panic("internal error: in and dst size does not match")
+		panic("internal error: in and dst size do not match")
 	}
 	size := -1
 	for i := range in {
@@ -291,7 +291,7 @@ func readShards(dst [][]byte, in []io.Reader) error {
 
 func writeShards(out []io.Writer, in [][]byte) error {
 	if len(out) != len(in) {
-		panic("internal error: in and out size does not match")
+		panic("internal error: in and out size do not match")
 	}
 	for i := range in {
 		if out[i] == nil {
@@ -318,7 +318,7 @@ type readResult struct {
 // cReadShards reads shards concurrently
 func cReadShards(dst [][]byte, in []io.Reader) error {
 	if len(in) != len(dst) {
-		panic("internal error: in and dst size does not match")
+		panic("internal error: in and dst size do not match")
 	}
 	var wg sync.WaitGroup
 	wg.Add(len(in))
@@ -366,7 +366,7 @@ func cReadShards(dst [][]byte, in []io.Reader) error {
 // cWriteShards writes shards concurrently
 func cWriteShards(out []io.Writer, in [][]byte) error {
 	if len(out) != len(in) {
-		panic("internal error: in and out size does not match")
+		panic("internal error: in and out size do not match")
 	}
 	var errs = make(chan error, len(out))
 	var wg sync.WaitGroup