travis: use cached nim instead of docker

.travis.yml

@@ -1,28 +1,22 @@
-language: c
-env:
-  - BRANCH=devel
-compiler:
-  - gcc
-  - clang
-before_install:
-  - |
-    if [ ! -x nim-$BRANCH/bin/nim ]; then
-      git clone -b $BRANCH --depth 1 git://github.com/nim-lang/nim nim-$BRANCH/
-      cd nim-$BRANCH
-      sh ci/build.sh
-      ./koch tools -d:release
-    else
-      cd nim-$BRANCH
-      git fetch origin
-      if ! git merge FETCH_HEAD | grep "Already up-to-date"; then
-        bin/nim c koch
-        ./koch boot -d:release
-        ./koch tools -d:release
-      fi
-    fi
-    export PATH=$PWD/bin:$PATH
-    cd ..
-script:
-  - nimble install -y
-  - nimble test
+language: c # or other C/C++ variants
+
+sudo: false
+
+# https://docs.travis-ci.com/user/caching/
+cache:
+  directories:
+    - nim
+
+os:
+  - linux
+  - osx
+
+install:
+  # build nim from our own branch, to avoid downtime due to nim regressions
+  - "export NIMVER=$(git ls-remote https://github.com/status-im/nim.git HEAD | cut -f 1)"
+  - "{ [ -f nim/$NIMVER/bin/nim ] && [ -f nim/$NIMVER/bin/nimble ] ; } || { rm -rf nim ; mkdir -p nim; git clone https://github.com/status-im/nim.git nim/$NIMVER; cd nim/$NIMVER; sh build_all.sh; cd ../.. ; }"
+  - "export PATH=$PWD/nim/$NIMVER/bin:$PATH"
+
+script:
+  - nimble install -dy && nimble test