Update libgit2 dependencies

Pulls in a few fixes for libgit2, including some security-related
updates.

Author: alexcrichton

Diff for: Cargo.toml

@@ -31,8 +31,8 @@ failure = "0.1.5"
 filetime = "0.2"
 flate2 = { version = "1.0.3", features = ['zlib'] }
 fs2 = "0.4"
-git2 = "0.9.2"
-git2-curl = "0.10.1"
+git2 = "0.10.0"
+git2-curl = "0.11.0"
 glob = "0.3.0"
 hex = "0.3"
 home = "0.4.2"
@@ -42,7 +42,7 @@ jobserver = "0.1.13"
 lazycell = "1.2.0"
 libc = "0.2"
 log = "0.4.6"
-libgit2-sys = "0.8.2"
+libgit2-sys = "0.9.0"
 memchr = "2.1.3"
 num_cpus = "1.0"
 opener = "0.4"