Trim whitespace between +a azimuth and others

Co-Authored-By: Dongdong Tian <seisman.info@gmail.com>

pygmt/base_plotting.py

@@ -432,8 +432,8 @@ def grdimage(self, grid, **kwargs):
             Give the name of a grid file with intensities in the (-1,+1) range,
             or a constant intensity to apply everywhere (affects the ambient
             light). Alternatively, derive an intensity grid from the input data
-            grid via a call to `grdgradient`; append **+a** \\ *azimuth*,
-            **+n** \\ *args*, and **+m** \\ *ambient* to specify azimuth,
+            grid via a call to `grdgradient`; append **+a**\\ *azimuth*,
+            **+n**\\ *args*, and **+m**\\ *ambient* to specify azimuth,
             intensity, and ambient arguments for that module, or just give
             **+d** to select the default arguments (``+a-45+nt1+m0``). If you
             want a more specific intensity scenario then run `grdgradient`