Remove extra - from fibers.

Dockerfile

@@ -18,7 +18,7 @@ ENV METEOR_RELEASE ${METEOR_RELEASE:-1.4.4.1}
 ENV USE_EDGE ${USE_EDGE:-false}
 ENV METEOR_EDGE ${METEOR_EDGE:-1.5-beta.17}
 ENV NPM_VERSION ${NPM_VERSION:-5.0.3}
-ENV FIBERS_VERSION ${FIBERS_VERSION:-1.0.15}
+ENV FIBERS_VERSION ${FIBERS_VERSION:1.0.15}
 ENV ARCHITECTURE ${ARCHITECTURE:-linux-x64}
 ENV SRC_PATH ${SRC_PATH:-./}