Upgrade some dependency versions

For now, the networking dependencies are being left alone, until they stabilise around Tokio v0.3.

Cargo.lock

@@ -485,9 +485,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.79"
+version = "0.2.80"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2448f6066e80e3bfc792e9c98bf705b4b0fc6e8ef5b43e5889aff0eaa9c58743"
+checksum = "4d58d1b70b004888f764dfbf6a26a3b0342a1632d33968e4a179d8011c760614"
 
 [[package]]
 name = "log"
@@ -500,9 +500,9 @@ dependencies = [
 
 [[package]]
 name = "memchr"
-version = "2.3.3"
+version = "2.3.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3728d817d99e5ac407411fa471ff9800a778d88a24685968b36824eaf4bee400"
+checksum = "0ee1c47aaa256ecabcaea351eae4a9b01ef39ed810004e298d2511ed284b1525"
 
 [[package]]
 name = "miniz_oxide"
@@ -778,18 +778,18 @@ checksum = "41cc0f7e4d5d4544e8861606a285bb08d3e70712ccc7d2b84d7c0ccfaf4b05ce"
 
 [[package]]
 name = "regex"
-version = "1.4.1"
+version = "1.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8963b85b8ce3074fecffde43b4b0dded83ce2f367dc8d363afc56679f3ee820b"
+checksum = "38cf2c13ed4745de91a5eb834e11c00bcc3709e773173b2ce4c56c9fbde04b9c"
 dependencies = [
  "regex-syntax",
 ]
 
 [[package]]
 name = "regex-syntax"
-version = "0.6.20"
+version = "0.6.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8cab7a364d15cde1e505267766a2d3c4e22a843e1a601f0fa7564c0f82ced11c"
+checksum = "3b181ba2dcf07aaccad5448e8ead58db5b742cf85dfe035e2227f137a539a189"
 
 [[package]]
 name = "remove_dir_all"
@@ -896,9 +896,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "1.0.45"
+version = "1.0.48"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ea9c5432ff16d6152371f808fb5a871cd67368171b09bb21b43df8e4a47a3556"
+checksum = "cc371affeffc477f42a221a1e4297aedcea33d47d19b61455588bd9d8f6b19ac"
 dependencies = [
  "proc-macro2",
  "quote",