env: remove file prefix from requirements

Signed-off-by: Alessandro Comodi <acomodi@antmicro.com>

docs/environment.yml

diff --git a/docs/environment.yml b/docs/environment.yml
index d669a56..e79e4fb 100644
--- a/docs/environment.yml
+++ b/docs/environment.yml
@@ -25,4 +25,4 @@
 - sphinx_rtd_theme
 # Packages installed from PyPI
 - pip:
-  - -r file:requirements.txt
+  - -r requirements.txt