package/ci: re-enable important plugins in the GLES build.

Those were disabled as they don't contain any ES-specific code to test,
however they are needed by various GL rendering tests.

package/ci/travis-desktop-gles.sh

@@ -31,16 +31,18 @@ cmake .. \
     -DWITH_WINDOWLESS${PLATFORM_GL_API}APPLICATION=ON \
     -DWITH_${PLATFORM_GL_API}CONTEXT=ON \
     -DWITH_OPENGLTESTER=ON \
+    `# Some plugins have to be enabled in order to test rendering output` \
+    `# Converter plugins are needed by the DebugTools::screenshot() test` \
     -DWITH_ANYAUDIOIMPORTER=OFF \
-    -DWITH_ANYIMAGECONVERTER=OFF \
-    -DWITH_ANYIMAGEIMPORTER=OFF \
+    -DWITH_ANYIMAGECONVERTER=ON \
+    -DWITH_ANYIMAGEIMPORTER=ON \
     -DWITH_ANYSCENECONVERTER=OFF \
     -DWITH_ANYSCENEIMPORTER=OFF \
     -DWITH_MAGNUMFONT=ON \
     -DWITH_MAGNUMFONTCONVERTER=ON \
     -DWITH_OBJIMPORTER=OFF \
-    -DWITH_TGAIMAGECONVERTER=OFF \
-    -DWITH_TGAIMPORTER=OFF \
+    -DWITH_TGAIMAGECONVERTER=ON \
+    -DWITH_TGAIMPORTER=ON \
     -DWITH_WAVAUDIOIMPORTER=OFF \
     -DWITH_DISTANCEFIELDCONVERTER=OFF \
     -DWITH_FONTCONVERTER=OFF \