Update Rust in Dockerfile to 1.49.0

rclrs_examples fail to compile due to the following error
```
error[E0658]: use of unstable library feature 'renamed_spin_loop'
  --> /usr/local/cargo/registry/src/gb.xjqchip.workers.dev-1ecc6299db9ec823/spin-0.9.2/src/relax.rs:26:9
   |
26 |         core::hint::spin_loop();
   |         ^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #55002 <rust-lang/rust#55002> for more information

   Compiling bitvec v0.19.5
error: aborting due to previous error
```

As seen in the noted link, updating Rust can resolve the issue. This
updates Rust in the Dockerfile to 1.49.0, where the issue seems to be
resolved.

Author: christopherjreid

Dockerfile

@@ -54,7 +54,7 @@ RUN apt-get update && apt-get install -q -y \
 ENV RUSTUP_HOME=/usr/local/rustup \
     CARGO_HOME=/usr/local/cargo \
     PATH=/usr/local/cargo/bin:$PATH \
-    RUST_VERSION=1.47.0
+    RUST_VERSION=1.49.0
 RUN set -eux; \
     wget -O rustup-init "https://sh.rustup.rs"; \
     chmod +x rustup-init; \