CI: Specify dir containing nlohmann_jsonConfig.cmake explicitly.

.drone.yml

@@ -21,12 +21,13 @@ steps:
     CXXFLAGS: -pipe -O2
     DEBIAN_FRONTEND: noninteractive
     LANG: C.utf8
+    nlohmann_json_DIR: "/usr/lib/cmake"
   commands:
   - rm /etc/apt/apt.conf.d/docker-clean
   - alias apt-get='rm -f /var/cache/apt/archives/lock && apt-get'
   - apt-get update -q
   - apt-get install -qq build-essential cmake clang pkg-config
-  - apt-get install -qq catch libcgicc-dev nlohmann-json3-dev
+  - apt-get install -qq catch libcgicc-dev nlohmann-json-dev
   - rm -rf build && mkdir -p build && cd build
   - cmake -G "Unix Makefiles" -DWITH_TESTS=YES ..
   - make VERBOSE=1