Merge #1178: Pin serde to 1.0.142

7a28a56 Pin `serde` to 1.0.142 (Martin Habovstiak)

Pull request description:

  1.0.143 bumps MSRV higher than what we support.

  Closes #1175

  Unfortunately I have to go now, will try to get back ASAP.

ACKs for top commit:
  apoelstra:
    ACK 7a28a56
  tcharding:
    ACK 7a28a56

Tree-SHA512: 09546984d3d68c24068cb357e4a57db223cea6b48e32471fab551998d8afe46eeaac2e6a49ec3d8bf2cc9767b564f12ccd6022ef8167d8e5eefdc6c898f3077a

contrib/test.sh

@@ -24,6 +24,9 @@ fi
 
 # We should not have any duplicate dependencies. This catches mistakes made upgrading dependencies
 # in one crate and not in another (e.g. upgrade bitcoin_hashes in bitcoin but not in secp).
+cargo update -p serde --precise 1.0.142
+cargo update -p serde_test --precise 1.0.142
+cargo update -p serde_derive --precise 1.0.142
 duplicate_dependencies=$(cargo tree  --target=all --all-features --duplicates | wc -l)
 if [ "$duplicate_dependencies" -ne 0 ]; then
     echo "Dependency tree is broken, contains duplicates"
@@ -118,6 +121,8 @@ then
     cargo new dep_test
     cd dep_test
     echo 'bitcoin = { path = "..", features = ["serde"] }' >> Cargo.toml
+    cargo update -p serde --precise 1.0.142
+    cargo update -p serde_derive --precise 1.0.142
 
     cargo test --verbose
 fi