Use spritesheets to reduce time spent sending PNG assets by 90+%

tools/travis/build_dependencies.sh

@@ -6,9 +6,12 @@ if [ "$BUILD_TOOLS" = false ]; then
     curl https://sh.rustup.rs -sSf | sh -s -- -y --default-host i686-unknown-linux-gnu
     source ~/.profile
 
-    git clone --branch $RUST_G_VERSION https://github.com/tgstation/rust-g
-
+    mkdir rust-g
     cd rust-g
+    git init
+    git remote add origin https://github.com/tgstation/rust-g
+    git fetch --depth 1 origin $RUST_G_VERSION
+    git checkout FETCH_HEAD
     cargo build --release
 
     mkdir -p ~/.byond/bin