Fix Travis CI for Leptonica 1.74.2

Signed-off-by: Stefan Weil <sw@weilnetz.de>

.travis.yml

@@ -45,8 +45,8 @@ before_install:
 install:
   #- if [[ $LINUX && "$CXX" = "g++" ]]; then export CXX="g++-6" CC="gcc-6"; fi
   - if test ! -d leptonica-$LEPT_VER/src; then curl -Ls https://github.com/DanBloomberg/leptonica/archive/$LEPT_VER.tar.gz | tar -xz; fi
-  - if test ! -d leptonica-$LEPT_VER/build/src; then cmake -Hleptonica-$LEPT_VER -Bleptonica-$LEPT_VER/build; fi
-  - if test ! -e leptonica-$LEPT_VER/build/src/libleptonica.so; then make -C leptonica-$LEPT_VER/build; fi
+  - if test ! -d leptonica-$LEPT_VER/usr; then cmake -Hleptonica-$LEPT_VER -Bleptonica-$LEPT_VER/build -DCMAKE_INSTALL_PREFIX=leptonica-$LEPT_VER/usr; fi
+  - if test ! -e leptonica-$LEPT_VER/usr/lib/libleptonica.so; then make -C leptonica-$LEPT_VER/build install; fi
 
 script:
   - mkdir build