Update to rust 0.6.
Update to rust 0.6.

ruud-v-a/rust-harfbuzz,klutzy/rust-harfbuzz,ruud-v-a/rust-harfbuzz,ruud-v-a/rust-harfbuzz,klutzy/rust-harfbuzz,larsbergstrom/rust-harfbuzz,larsbergstrom/rust-harfbuzz,klutzy/rust-harfbuzz,ruud-v-a/rust-harfbuzz,klutzy/rust-harfbuzz,larsbergstrom/rust-harfbuzz,ruud-v-a/rust-harfbuzz,larsbergstrom/rust-harfbuzz,klutzy/rust-harfbuzz,larsbergstrom/rust-harfbuzz