Upgrade to Rust 1.48.0

ci/docker-rust-nightly/Dockerfile

@@ -1,4 +1,4 @@
-FROM solanalabs/rust:1.46.0
+FROM solanalabs/rust:1.48.0
 ARG date
 
 RUN set -x \

ci/docker-rust/Dockerfile

@@ -1,6 +1,6 @@
 # Note: when the rust version is changed also modify
 # ci/rust-version.sh to pick up the new image tag
-FROM rust:1.46.0
+FROM rust:1.48.0
 
 # Add Google Protocol Buffers for Libra's metrics library.
 ENV PROTOC_VERSION 3.8.0

ci/rust-version.sh

@@ -18,13 +18,13 @@
 if [[ -n $RUST_STABLE_VERSION ]]; then
   stable_version="$RUST_STABLE_VERSION"
 else
-  stable_version=1.46.0
+  stable_version=1.48.0
 fi
 
 if [[ -n $RUST_NIGHTLY_VERSION ]]; then
   nightly_version="$RUST_NIGHTLY_VERSION"
 else
-  nightly_version=2020-08-17
+  nightly_version=2020-12-13
 fi