Replace getrandom with rand_core (#276)

`rand_core::OsRng` provides a facade over `getrandom` which simplifies
error handling.

Cargo.lock

@@ -277,17 +277,6 @@ dependencies = [
  "version_check",
 ]
 
-[[package]]
-name = "getrandom"
-version = "0.1.16"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8fc3cb4d91f53b50155bdcfd23f6a4c39ae1969c2ae85982b135750cccaf5fce"
-dependencies = [
- "cfg-if",
- "libc",
- "wasi 0.9.0+wasi-snapshot-preview1",
-]
-
 [[package]]
 name = "getrandom"
 version = "0.2.3"
@@ -296,7 +285,7 @@ checksum = "7fcd999463524c52659517fe2cea98493cfe485d10565e7b0fb07dbba7ad2753"
 dependencies = [
  "cfg-if",
  "libc",
- "wasi 0.10.2+wasi-snapshot-preview1",
+ "wasi",
 ]
 
 [[package]]
@@ -632,7 +621,7 @@ version = "0.6.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d34f1408f55294453790c48b2f1ebbb1c5b4b7563eb1f418bcfcfdbb06ebb4e7"
 dependencies = [
- "getrandom 0.2.3",
+ "getrandom",
 ]
 
 [[package]]
@@ -893,7 +882,7 @@ version = "0.8.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bc5cf98d8186244414c848017f0e2676b3fcb46807f6668a97dfe67359a3c4b7"
 dependencies = [
- "getrandom 0.2.3",
+ "getrandom",
 ]
 
 [[package]]
@@ -902,12 +891,6 @@ version = "0.9.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5fecdca9a5291cc2b8dcf7dc02453fee791a280f3743cb0905f8822ae463b3fe"
 
-[[package]]
-name = "wasi"
-version = "0.9.0+wasi-snapshot-preview1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cccddf32554fecc6acb585f82a32a72e28b48f8c4c1883ddfeeeaa96f7d8e519"
-
 [[package]]
 name = "wasi"
 version = "0.10.2+wasi-snapshot-preview1"
@@ -989,7 +972,6 @@ dependencies = [
  "des",
  "elliptic-curve",
  "env_logger",
- "getrandom 0.1.16",
  "hmac",
  "lazy_static",
  "log",
@@ -1001,6 +983,7 @@ dependencies = [
  "p384",
  "pbkdf2",
  "pcsc",
+ "rand_core",
  "rsa",
  "secrecy",
  "sha-1",