Don't always build code coverage

.travis.yml

@@ -41,21 +41,23 @@ script:
 after_script: set +e
 after_success: |
     # Build test coverage statistics
-    wget https://github.com/SimonKagstrom/kcov/archive/master.tar.gz && \
-    tar xzf master.tar.gz && \
-    cd kcov-master && \
-		mkdir build && \
-		cd build && \
-		cmake .. && \
-		make && \
-		make install DESTDIR=../../kcov-build && \
-    rm -rf kcov-master && \
-    for file in target/debug/*-*[^\.d]; do \
-      mkdir -p "target/cov/$(basename $file)"; \
-      ./kcov-build/usr/local/bin/kcov --exclude-pattern=/.cargo,/usr/lib --verify "target/cov/$(basename $file)" "$file"; \
-    done && \
-    bash <(curl -s https://codecov.io/bash) && \
-    echo "Uploaded code coverage"
+    if [ -z "$CODECOV" ]; then
+        wget https://github.com/SimonKagstrom/kcov/archive/master.tar.gz && \
+        tar xzf master.tar.gz && \
+        cd kcov-master && \
+            mkdir build && \
+            cd build && \
+            cmake .. && \
+            make && \
+            make install DESTDIR=../../kcov-build && \
+        rm -rf kcov-master && \
+        for file in target/debug/*-*[^\.d]; do \
+          mkdir -p "target/cov/$(basename $file)"; \
+          ./kcov-build/usr/local/bin/kcov --exclude-pattern=/.cargo,/usr/lib --verify "target/cov/$(basename $file)" "$file"; \
+        done && \
+        bash <(curl -s https://codecov.io/bash) && \
+        echo "Uploaded code coverage"
+    fi
 
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